To determine whether prevalence and intensity of infection are factors in morbidity in schistosomiasis japonica, a cross-sectional study was undertaken in three villages in Leyte, Philippines, namely, Santol (A), Santa Rosa (B), and Macanip (C). Kato thick-smear fecal examination and egg counts were made on 289 of 341 residents in Village A (85%), 824 of 1,008 in Village B (82%), and 1,113 of 1,241 in Village C (90%). Prevalences of 26%, 39%, and 44%, respectively, were found in the three villages, the majority of their populations (56-74%) remaining uninfected. Most of the infected persons (17-30% of the total population) had light infections (10-100 eggs/g feces). Moderately infected persons (101-400 eggs/g) comprised a smaller segment (7-14%), while a very small proportion (2-7%) had heavy infections (greater than or equal to 401 eggs/g). Age prevalence and egg excretion peaked earlier in the areas with higher prevalence (B and C) than in the area with the lowest prevalence (A). There was no relationship between area prevalence and mean egg count. Symptoms of inability to work, weakness, abdominal pain, and diarrhea correlated with the presence of infection in the area with the highest prevalence (C), but not in the area with the lowest prevalence (A). Except for diarrhea, there was no relationship between symptoms and intensity of infection. Very few persons presented with hepatomegaly and/or splenomegaly (1-5%). The frequency of liver enlargement on the midsternal (measuring 3-6 cm and 6 cm or more) and midclavicular line (2-4 cm), as well as spleen enlargement (Hackett 2 or greater), correlated with the presence but not with the intensity of infection. Hepatomegaly was sex- and age-related, being most common among males and among adolescents aged 10-14 years.