Two chimpanzees were born to parents with chronic non-A, non-B hepatitis and remained with their mothers until 12 and 18 months, respectively. The infants were followed from 7 to 8 weeks of age with biweekly or monthly blood samples and with monthly liver biopsies from 4 to 7 months after birth. Another chimpanzee, along with both of its parents, was held throughout the parents' acute infection with non-A, non-B hepatitis; at this time the infant was 14-16 months of age, and it was followed with bi-weekly blood samples and monthly biopsies from the time of potential exposure for 20 months. No abnormalities indicative of non-A, non-B hepatitis were detected in these animals. During the 29 to 35 months of follow-up, alanine aminotransferases and gamma glutamyl-transferases (GGPT) levels remained well within normal range for animals held in the same facility. Histologic and electron microscopic examination of liver tissue revealed no abnormalities.