The relationship of bilirubin (a red bile pigment that is sometimes found in the urine and occurs in the blood and tissues in jaundice) in infancy to later intellectual development was investigated in 241 infants with moderately elevated and high bilirubin levels. Ss were administered motor, psycholinguistic, and intelligence tests at age 8 months, 4 years, and 7 years. High bilirubin levels were found to be significantly associated with decreased mental and motor development at 8 months of age. There were no significant differences on measures of intellectual development at 4 and 7 years of age. (A review of previous research on the subject is presented.) (SBH)