We studied the effect of ciclosporin (Cs) on rats which underwent a 90% hepatectomy. Rats were divided into two groups: group 1 (without Cs pretreatment) and group 2 (with Cs pretreatment). Animals were given a 4-day treatment of Cs (10 mg/kg/day) prior to hepatectomy. The 1-week survival, serum biochemistry and parameters for hepatocyte proliferation (indices for mitosis and 5-bromo-2-deoxyuridine uptake) were serially investigated. Although Cs pretherapy significantly upregulated liver cell proliferation in group 2, there was no improvement in the survival rate of the immunosuppressed animals (group 2) compared to the controls (group 1). The implications of Cs pretherapy are discussed in the setting of extensive hepatectomy.