Objective: To evaluate the growth, feeding and health of babies fed a novel infant formula milk with added long chain polyunsaturated fatty acids (LCPs) produced from single-cell sources, at concentrations similar to those found in mature breast milk. Design: Randomized double-blind control trial. Subjects: One-hundred and forty healthy, full-term infants of birth weight 2.5 ± 4.5 kg born at the Maternity Department, East Glamorgan General Hospital, Wales, whose mothers had already decided to bottle feed. Interventions: Subjects were randomized to two groups; one (control group) to receive a standard formula milk and the other to receive the trial milk with added LCPs. Milks were supplied in a double-blind fashion and given for the ®rst 12 weeks of life. Anthropometric measurements were made at recruitment, 3 months, 6 months and 1 y. Feeding diaries were completed at 6 weeks and 3 months, and a parental record was kept of any ill health suffered by the subjects during the ®rst year of life. Results: Of 140 infants recruited, 31 did not complete the protocol. Small but statistically signi®cant differences were found only in the subscapular skinfold thickness at 6 weeks and 3 months, that in the trial group being slightly higher, but unlikely to be of any clinical importance. No differences were found in the feeding patterns of the infants in the two groups. Stool patterns were similar, as were the frequencies of illness and allergy. Conclusions: This study supports the view that LCPs from single-cell sources do not have detrimental effects on the growth, feeding and general health of infants.