Eighteen patients with solid tumours were treated with human recombinant interferon-gamma at escalating dose levels starting at 1 X 10(6) units/m2 per infusion and rising through 3 X 10(6), 6 X 10(6), 9 X 10(6) and 22 X 10(6) to a maximum of 110 X 10(6) units/m2 per infusion. The IV infusions were given three times a week over a 4-week period. Side effects were seen in all patients, but were mild except at the highest dose. Acute dose-related effects included pyrexia, tiredness, thirst, chills and rigors. Chronic dose-related effects included anorexia, lethargy, weakness, disorientation, a trace of proteinuria and minimal rises in liver enzymes. In addition, effects were observed which were not related to dose. These included headache, nausea and vomiting, backache, myalgia, flatulence and a mild, transient reduction in neutrophils and erythrocytes. At the highest dose level dose-limiting toxicity was observed, consisting in severe tiredness and anorexia, hypotension, disorientation and changes on the electrocardiograph. Overall, toxicity was similar to that seen with preparations of interferon-alpha, except that no tolerance to the effects of interferon-gamma was noted. We observed less hepatic and haematological toxicity, but also recorded flatulence, handcramps and electrocardiograph changes, which have not been reported with interferon-alpha. When given according to this regimen, doses of 22 X 10(6) units/m2 per infusion of recombinant interferon-gamma were generally well tolerated by the patients.