Variations in fecal Schistosoma japonicum egg counts were studied in ZhuXi administrative village. JiangXi Province. China. Population stool examinations were collected with duplicate, standard, 41.5mg Kato-Katz thick smears on seven consecutive days for 570 individuals from two natural (individual) vifinges: village I with high endemieily and village Ⅱ with low endemicity. The peoportion of individuals with at least tree posirive count increased from 42.4% after a single measurement to 68.3% after seven measurements in village I (n=356), and from 17.0%, to 36.0% in village Ⅱ (n=214). respectively. This demonstrates a very high variation in repeated S. japonicum egg counts and a eonsiderable lack of sensitivfty of the Kato-Katz teehnique: fight and moderate infections are especially missed widi a single or a few measurements. The observed day-to-day variation in individual egg counts is highly aggregated (varianee higher than the mean) and suggestive of a negative binomial distribution. For rive individuals on dace days. repeated sampling from different locations of a stool specimen shows a clear trend widi egg euunts deereasing from the beginning of the stool to the end and from the outside layer to the center. Ten muhiple samples from a particuhar subsection (10-30g) of a stoool specimen for 44 posirive individuals still showed aggregation in egg counts, particularly for high intensities of infection. This means diat the aggregnlion in repeated diliiy S. japomcium egg counts cannot be explained alone by a specific day-to-day component and variation in die eoneenration of eggs at differem locations in the stood, There also exists clustering of eggs within paris of The strol.