The incidence of atopic manifestations was analyzed in infants "at risk" because of histories of atopy in first degree relatives. The incidence of atopic manifestations was significantly reduced (P = .0011) during the first 6 months of life when only the whey hydrolysate was administered (2/32 infants, 6.3%) compared with the incidence when an adapted formula was given (14/35 infants, 40%). This beneficial effect continued during the 6 to 12-month period, after diversification of the diet at 6 months. At the age of 1 year, 7/32 (21.8%) of the infants in the whey hydrolysate group had presented with manifestations of probable atopic disease compared with 17/35 (48.6%) infants in the adapted formula group (P = .021). The incidence of cow milk protein sensitivity was evaluated at 5/32 (15.6%) in the hydrolysate group and 15/35 (42.8%) in the adapted formula group (P = .014). Other foods such as egg and fish may be responsible for manifestations in three infants in hydrolysate group and in five infants of the adapted group (9.4% and 14.3%, respectively NS). These preliminary data show that the administration of a whey hydrolysate during the first 6 months of life to babies "at risk" decreased the incidence of atopic disease up to the age of 12 months. The incidence of cow milk protein sensitivity appeared to be decreased, whereas the incidence of sensitivities to other food proteins was comparable in both groups.