The immunosuppressive qualities and other features of a new cyclosporine (CsA) analogue, Nva2-cyclosporine (Nva2-CsA) were examined using canine orthotopic liver allografts. The mean survival time was 11.8 +/- 9.6 (SD) days in dogs without treatment, 60.8 +/- 4.4 days with Nva2-CsA and 65.1 +/- 33.0 days with CsA. Functional abnormalities indicating toxic side effects were not noted either with Nva2-CsA or with CsA. Using the same oral dose, the rate of blood level rise and the amount of the rise were greater with Nva2-CsA. Histopathologically, Nva2-CsA treatment was associated with the same degree of hydropic vocuolation in the pars recta of the proximal tubules as CsA treatment. Thus, in the dog, Nva2-CsA had identical immunosuppressive properties as CsA, with no functionally detectable toxicity affecting the liver and kidney.