The use of cyclosporine long term after orthotopic liver transplantation has been analyzed in 73 adults with particular reference to the dose of drug used, either alone or in combination with other immunosuppressive agents, and the side effects observed. The first 22 patients were given cyclosporine 10 mg/kg/day for up to 2 years, but thereafter in these, and in all the other patients, the drug dose was regulated by whole blood trough levels. The proportion of patients maintained on cyclosporine alone increased from 11% at 3 months to 54.9% and 55.6% at 3 and 4 years, respectively. The dose of prednisolone used in combination with cyclosporine was lower than that used with azathioprine (P less than 0.05) up to 12 months after transplantation, but thereafter no significant difference was found. Acute cellular rejection was seen in 5 patients and in all instances was related to cessation of cyclosporine, while 10 patients developed chronic graft rejection manifested by the vanishing bile duct syndrome. At 12 months and onward, 54.5-73.3% of patients had normal serum bilirubin levels, and 47.6-80.0% had aspartate aminotransferase levels in the normal range. Cyclosporine was discontinued in 12 patients, in 8 cases because of impairment of renal function or hypertension. A trend toward rising serum creatinine levels was seen, and after 4 years on cyclosporine none of 12 patients had normal levels, and these exceeded 200 mumol/L in 5. The rise in creatinine levels was probably in part related to the higher doses used early in the study period. The incidence of hypertension progressively increased from 15.3% at 3 months to 63.6% at 4 years in patients maintained on cyclosporine.