1. The camel has insulin receptors that by multiple function criteria are very similar to those of the other mammals (rabbit and rat) and non-mammals (chicken and pigeon), with sharp pH dependence to insulin binding at pH 7.2-7.6. 2. Equilibrium binding was faster at higher temperatures (24-37 degrees C) than at lower (4 degrees C). 3. Binding data yielded curvilinear Scatchard plots with half maximal displacement of 125I-insulin at 9 x 10(-9) M, 2.5 x 10(-9) M, 6.3 x 10(-10) M for camel, rabbit, pigeon and chicken respectively, suggesting differences in mammalian and non-mammalian liver membranes. 4. Autoradiogram patterns showed the presence of an identical subunit structure with Mr 74,000 for all membranes studied. Pigeon membrane showed a band with Mr 110,000, the absence of which in other membranes could be due to the degradation factor or the concentration of disuccinimidyl suberate (DSS).