Commercial pasteurized, UHT and sterilized milk samples, and laboratory autoclaved milks, were analysed for lactulose by an enzymatic method. No lactulose was detected in the pasteurized milk. On the basis of the measured lactulose concentrations, the UHT and sterilized milk samples fell into five groups according to the type of process that they had received.The lactulose concentrations in the laboratory autoclaved milks rose on storage, but this was not observed in the other milks.It appears that pasteurized, UHT and sterilized milks can be differentiated by their lactulose content.