Abstract: A quantitative study on the probability of the dispersion of schistosome eggs into Oncomelania-infested water bodies was carried out during 1980-1982 in a plain region of schistosomiasis endemic area by field survey and simulated experiments. The results showed that the daily estimated number of eggs contaminating the snail-infested water bodies was approximately 12 671.58 in summer and 9 711.08 in other seasons, accounting for approximately 0.996 and 0.6996 of the total daily fecal egg output respectively in the 4 villiages investigated.Quantitative comparison of different ways of egg contamination showed that the washing of commodes is of greatest importance. Direct defecation of tattle into water bodies and fertilization of the fields nearby the streams are of secondary importance while the cleaning of nightsoil buckets and dippers and promiscuous feces are of minor significance. However, in summer, the overflow of the night soil jars nearby the water body plays an important role just next to the washing of commodes.