49 Sudanese schoolchildren aged 6-9 years with Schistosoma mansoni infection were ultrasonographically examined by two independent observers in a double-blind fashion. The first observer recorded normal appearance of the liver in 23 cases, whereas the second observer recorded the appearance as normal in 33 cases. There were 23 concordant observations. For Grade I periportal fibrosis (PF), 13 observations were concordant. PF Grade II was rarely observed (2 versus 3 cases), and Grade III was not recorded at all. In total, 38 out of 49 observations were concordant (77.5%). These preliminary data from two ultrasound observers, from observations on a limited number of patients, can be seen as an indication of a potential inter-observer variation of around 20% for the distinction between the absence of PF and a low level of PF.