The DNA sequence of a chicken leptin gene that shares 95% nucleotide similarity with the mouse leptin sequence has been recently reported (Taouis et al., 1998, Gene 208, 239-242). Experiments have been performed independently in two laboratories to try to confirm this finding. Fourteen PCR primers based on the mouse leptin sequence were designed to amplify the avian leptin gene. Four of the primers were identical to the mouse and published chicken leptin sequences. PCR amplification was carried out on genomic DNA and reverse-transcribed mRNA from the fat, liver, and pancreas of several chicken strains and from the domestic turkey, goose, and Japanese quail. No PCR products sharing close similarity to the mouse leptin sequence were generated from any avian templates. Amplification of mouse leptin sequence was consistently obtained when control mouse templates were used. Northern hybridization using a mouse leptin probe failed to produce a signal with poly(A)+ RNA from chicken fat and liver and from the fat and liver of force-fed geese but a strong signal was obtained from control mouse fat total RNA. Southern hybridization under low stringency washing conditions revealed hybridization of a mouse leptin probe to chicken genomic DNA. Under higher stringency washing conditions, the chicken signal disappeared, while those from control mouse and sheep genomic DNA remained. This suggests that the putative chicken leptin sequence shares less than the 83% nucleotide sequence identity between the mouse and sheep genes. It is concluded that a chicken leptin gene sequence with close sequence similarity to mouse leptin is not present in the chicken genome. Furthermore, mRNA sharing high sequence identity with mouse leptin is not present in the fat or liver of the domestic chicken, turkey, goose, or Japanese quail.