The immune suppressed lizard, Anolis carolinensis, can be used to test for in vivo tumor production by cell lines derived from a variety of ectothermic vertebrates. Cell lines tested for tumor production were also assessed for loss of attachment-dependent proliferation and contact inhibition of cell overlap. The results demonstrate that the criteria standardly used to assess transformation and neoplastic change in cultured mammalian cells apply equally well to cultured cells from ectotherms.