A laboratory procedure for sex identification of monomorphic birds was developed using modern cytological methods of detecting chromosome abnormalities in human amniotic fluid samples. A pin feather is taken from a pre-fledging bird for tissue culture and karyotype analysis. Through this method, the sex was identified and the karyotype described of the whooping crane (Grus americana) and the Mississippi sandhill crane (G. canadensis pulla). Giemsa-stained karyotypes of these species showed an identical chromosome constitution with 2n = 78 + 2. However, differences in the amount of centromeric heterochromatin were observed in the Mississippi sandhill crane when compared to the whooping crane C-banded karyotype.