The intestinal contents of a dog infected with 49,732 M. yokogawai for 8 weeks were normal but in a 4-week-old infection the intestinal water content correlated roughly with the number of worms. Most worms were found 40 to 102 cm along the small intestine but the entire length was parasitized. The concentrations of Na+, K+ and Cl- decreased and the concentration of HCO3- and pH increased along the small intestine while the osmolarity remained roughly constant (324 to 340 mOsm/kg).