Objective: To compare feeding tolerance, nutrient intake and growth in preterm infants (p32 weeks, p1750 g) fed either a standard nonhydrolyzed whey-casein (nHWC) or a partially hydrolyzed whey (pHW) preterm infant formula.Study Design: In this double-blind randomized controlled trial infants were fed either formula for at least 3 weeks. Intake was monitored daily, serum chemistries and growth weekly. Data were analyzed using analysis of covariance.Result: A total of 80 infants were enrolled, 72 completed the study. No differences were noted in demographic characteristics. No differences were detected in feeding tolerance, intakes (118 ± 21 vs 119 ± 14; nHWC vs pHW) or growth weight, 28 ± 1.5 vs 28 ± 1.6 g per day; length, 1.0 ± 0.7 vs 1.0±0.6 cm per week; head circumference, 0.9±0.4 vs 1.0±0.44 cm per week). At the end of study, blood urea nitrogen (5.2 ± 3.1 <6.7±2.3 mg per 100 ml, nHWC4.4 ± 0.5 g per 100 ml) and albumin (2.7 ± 0.3 >2.6 ± 0.4 g per 100 ml) differed. Conclusion:A pHW preterm infant formula was not associated with improved feeding tolerance, enteral intake or growth but differences in serum chemistries. These are unlikely to be clinically relevant because values were well within normal limits for preterm infants, whereas growth was identical in both groups and paralleled that 'in utero'.