The immunological and clinical results of a 2-year study of 16 patients with agammaglobulinaemia (common variable in 12 and sex-linked in 4) are reported. Plasmin-treated immunoglobulins were injected at 3 weeks' intervals during the first part of the trial and at 2 weeks' interval during the second part. An increase in serum IgG levels was observed after 24 hours and 7 days, with progressive return to initial values on the 14th day. Twelve patients showed signs of clinical improvement.