An analysis was made of clinical and laboratory findings in children with the diarrheal form of the hemolytic uremic syndrome (HUS) treated at The Children's Hospital, Birmingham between 1970 und 1987. From 1982 the rate of referral increased, the prodromal illness more often consisted of bloody diarrhea, and the mean age at presentation doubled from 2 to 4 years. For patients with a good outcome there was an excess of males in the period 1970-81, and females in the period 1982-87. Moreover, in the years 1982-87 the disorder was distinguished from that of the earlier time by a positive correlation between adverse outcome and both neutrophil leukocytosis and a higher hemoglobin concentration at presentation. Prognostic scores obtained by logistic regression analysis were specific for each period. From July 1983 stool samples were analyzed for verocytotoxin-producing Escherichia coli (VTEC) and neutralizable verotoxin. Positive results were obtained in 39% of cases. The nature of HUS has changed and the new form of the disorder is associated with VTEC infection.