The impact of bilharziasis on a community has been evaluated in terms of the stages and grades of severity of the disease; egg counts in faeces and urine were correlated with the clinical severity. At the time this study was carried out, the over-all prevalence of S. haematobium infection was 37.6%, that of S. mansoni infection 29.8% and that of mixed infections 17.1%.Of 579 people examined, 292 (58.2%) were excreting schistosome eggs. All except one person were classified as Stage III-asymptomatic, 122 (41.8% of those infected); mild, 74 (25.3%); moderate, 89 (30.5%); severe, 6 (2.1%). The remaining person was classified as Stage IV (moderate). Mixed infections produced a higher proportion of symptomatic cases (74.8%) than either infection alone (58.2%), and S. haematobium (57.1%) a higher proportion than S. mansoni (37.8%). The percentage of symptomatic cases was highest in those aged 10-14 years, who also had the highest prevalence of infection.On average, the egg output per infection was in the range 32-63 eggs for S. haematobium infections and 4-7 for S. mansoni in unit measure of urine and faeces, respectively. For S. haematobium infections, alone and in mixed infections, mean egg output increased with the severity of clinical symptoms. For S. mansoni infections, no such relation was established.It is concluded that the criteria of severity should be made more objective and that more satisfactory methods of determining egg counts should be adopted in an attempt to obtain more direct evidence of the validity of regarding egg count as a measure of worm load.