Normal serum creatinine (Scr) and creatinine clearance (Ccr) values during the first 10 days of life were obtained in 63 very premature (28-32 weeks of gestation), premature (33-37 weeks) and term infants (38-42 weeks). Scr fell, and Ccr rose less markedly in the very premature infants. Scr was 80 mumol/l on the 1st day of life both in very premature and premature infants, and 77 mumol/l in full-term neonates. After 10 days, Scr was 73, 53 and 35 mumol/l respectively. There was an exponential correlation between Ccr and gestational age, indicating rapid maturation of glomerular function.