This study was undertaken to evaluate the present status of intestinal helminthic infections in Koreans, from April 1967 through May 1969. The nationwidely collected stool specimens and scotch-tape anal swabs from primary schoolchildren, middle school students, draftees to army recruitment camp, soldiers and inhabitants of various parts of Korea were examined. The methods employed were Kato's cellophane thick smear technique and formalin-ether sedimentation technique in 40,581 for the prevalence rate of various intestinal helminths, scotch-tape anal swab technique in 8,585 for the prevalence rate of Enterobius vermicularis and by Stoll's dilution egg counting technique in 1,174 for the evaluation of the worm burden of some helminths. The results are as follows:

I. Result of stool examination

1. The positive rate of intesinal helminthes of any kind was 90.5% among 40,581. In rural people, it was 92.3% in average in contrast to 85.0% in Seoul inhabitants.

2. The infection rate of A. lumbricoides in 40,581 was 58.2%. It was higher in rural people 62.9% than in Seoul inhabitants and highest in 5-9 year-old group by age.

3. The infection of Trichocephalus trichiurus showed the highest prevalence rate in Koreans and it was 74.5%. No remarkable difference was observed between Seoul inhabitants(72.2%) and rural people(75.2%). The tendency of higher prevalence rate with the older age group was observed.

4. The infection rates of hookworm and Trichostrongylus orientalis in 40,581 examinations by cellophane thick smear were 5.1% and 5.8% respectively. But in 4,949 examinations for which refined cellophane thick smear technique and formalin-ether sedimentation technique were employed, the infection rates were turned out 17.6% in hookworm and 15.9% in T. orientalis. Although rural people showed higher infection rate of hookworm(18.8%) than Seoul inhabitants(13.8%), the reverse was true in T. orientalis infection rate(14.5% : 20.3%). Both kinds of infections were tend to be higher with the increase of age.

5. The infection rates of Clonorchis sinensis and Metagonimus yokogawai were 4.7% and 0.4% respectively. In both kinds of infections male showed higher infection rates than female and the tendencies of higher infection rate in the older age group were observed. The provinces which showed the higher infection rate of C. sinensis were South and North Kyongsang Do and North Cholla Do, all of which are provinces of southern part of Korea. Some endemic foci of M. yokogawai were noticed in South Kyongsang Do and South Cholla Do.

6. The infection rate of Taenia spp. by applying only the stool examination was 0.7% throughout the survey. No sex difference in infection rate of Taenia spp. was noticed, but in older age group it was increased. Cheju Do, the island of extreme southern part of Korea seemed the most endemic area and South and North Cholla Do were next in ranking of Taenia infection rate.

The ova of Hymenolepis nana were observed in 0.2% and all of them were under the age of 20 except only one caes. The infection rate seemed higher in female (0.3%: 0.1%). No geographical difference was noticed except 1.1% of schoolchilderen and students of Cheju Do.

II. Result of Scotch-tape anal swab technique for E. vermicularis infection.

The infection rate of E. vermicularis in 8,585 urban and rural schoolchildren and rural inhabitants was 46.6%. Female (57.9%) had definitely higher infection rate than male (41.4%). The infection rate was significantly higher in rural people than Seoul schoolchildren. The exteme example was 79.7% in schoolchildren of South Cholla Do.

III. Result of worm burden examination by Stoll's dilution egg-counting technique

1. Among 1,174 examinations, countable(E.P.G.> 100) cases of A. lumbricoides were 745(63.5%) and the mean E.P.G. was 9,723. The mean E.P.G. in Seoul inhabitants was 5,835 in contrast to 10,820 in rural people. The age group of 5-9 showed the heaviest mean E.P.G., 11,337. 70.6% of 745 cases were less than 10,000 in E.P.G. which means light infection.

2. Countable cases by Stoll's technique for T. trichiurus ova were 63.5% and mean E.P.G. was 649. No difference between Seoul and rural inhabitants was observed. Grade I and II in which E.P.G. is less than 5,000 involve 99.3% of positive cases.

3. 91 cases (7.9%) in 1,174 were positive for hookworm ova by Stoll's technique and mean E.P.G. was 501. All cases were in Grade I and II which were less than 5,000 in E.P.G. Trichostrongylus orientalis was positive only in 25 cases (2.1%) by Stoll's technique and mean E.P.G. was 340. No cases were found to have more than 5,000 in T. orientalis E.P.G.

4. The mean E.P.G. of Clonorchis sinensis among the referred cases of clonorchiasis to Department of Parasitology, Seoul National University, was 9,416. On the other hand mean E.P.G. of C. sinensis was 21,376 among cases in the hyperendemic area of Kimhae, South Kyongsang Do, and 3,073 in cases from other various localities. Among referred clonorchiasis cases to our Department, 21.6% were turned out to have the E.P.G. more than 10,000. The cases who have the E.P.G. more than 10,000 in hyperendemic area, Kimhae were 40.7% and in other various localities were 9.1%