Body weights were recorded at birth, 45 and 90 days on 199 Merino lambs. Serum samples were obtained and analysed with horizontal starch gel electrophoresis to identify the transferrin types. Sixteen transferrin phenotypes, TfAA, TfAB, TfAM, TfAD, TfAE, TfBB, TfBM, TfBD, TfBE, TfMM, TfMD, TfMS, TfME, TfDD, TfDE and TfEE were detected in this study. The phenotypes were confirmed on the basis of international nomenclatures. Lambs were grouped according to their transferrin types. The average weight of different groups at birth and the weight gains in the first and second 45-day periods were estimated. TfDE was the poorest weight gainer but the differential value was significant only in the second 45-day period.