N-acetyl-(14C)neuraminosyl-(α,2→3)lactose enzymatically prepared of CMP-NeuNAc and lactose by a particulate enzyme fraction from lactating rat mammary gland was applied orally to newborn rats and examined for uptake and distribution in relation to those of free N-acetyl-(14C)neuraminic acid. The neonates were allowed to stay with their mother before and during the incubation time up to 6 h. Within this time 70% of the given dose was excreted while 30% was retained in the body. (14C)NeuNAc-lactose activity appeared 1.5 h after application in blood, urine, and tissues and attained maximum values after 3 and 6 h, respectively. The highest uptake occurred in liver, spleen, and brain. The absorption of the trisaccharide was delayed by 30 min compared with free (14C)NeuNAc. The time courses of the curves show a slower but higher accumulation in the tissues suggesting a better utilization of the (14C)NeuNAc from (14C)NeuNAc-lactose or pecularities in the absorption of the trisaccharide by the orga