Cell cultures derived from the heart (GH-1) and lung (GL-1) of an adult male Tokay gekko (Gekko gecko) have been serially propogated for more than two years. Cytogenetic examination of primary cultures as well as various subcultures from different passage levels of both lines was undertaken. The diploid karyotype possesses 38 chromosomes with no evident heteromorphic pair in either sex nor presence of microchromosomes. In the cultured cells, a bimodal distribution of chromosome numbers (38 and 40) was evident in both the GH-1 and GL-1 lines. The same subtelocentric chromosome was affected in both lines. In the GH-1 line, this element appeared tetrasomic, but one member of the group appeared to have undergone a pericentric inversion. The GL-1 line also showed tetrasomy for this chromosome. Attempts to repeat this karyotypic alteration by thawing cells frozen at low passage levels were unsuccessful, although cells from these cultures possessing 39 chromosomes were trisomic for the subtelocentric chromosome.