Summary.-Twenty-four patients with advanced cancer not reacting to conventional therapy were treated with 97 courses of i.v. MER (methanol extraction residue of BCG). MER was administered by i.v. infusion over a 4-h period, twice a week, in dosages varying from 0-05 mg to 1 25 mg. The skin reactivity to 5 recall antigens was evaluated in the patients. All patients except 4 were anergic. Twelve patients had no side-effects. Anergic patients had less side-effects than ergic patients. The sideeffects recorded in the others were fever, chills, vomiting and tachycardia. The reaction subsided within 24 h after treatment and was tolerable for most patients.In 2 patients an objective improvement was observed. No changes in cutaneous reactivity, renal and hepatic functions were found. A significant increase in peripheral leucocyte count was noted in two patients and slight a increase in the remainder.