The study was designed to quantify the preterm baby's response to routine childhood immunisations. A total of 69 preterm babies were put into two groups according to their gestational age: less than 32 weeks and between 32 and 35 weeks. Within each group the babies were randomly placed into one of three schedules for immunisation with diphtheria, tetanus, pertussis and oral poliomyelitis vaccines at 3, 4 and 5 months; 3, 4, 5 and 18 months; and 3, 4 and 10 months. Antibodies were measured before immunisation, one month after the third vaccine dose and at age 19 months. Of these children, 30 had further antibody estimations when they were between 4 and 5 years of age. One month after the third immunisation and at 19 months of age all infants, independent of gestational age, had adequate immunity to the four infections. Children sampled before and after their pre-school booster, with few exceptions, showed persistence of protective antibody and an enhanced response to the booster dose respectively. No correction needs to be made for prematurity when initiating routine immunisation in premature infants.