Fourteen patients with metastatic carcinoid tumors were treated with recombinant interferon alpha-2b at a dosage of 3-4 x 10(6) IU s.c. daily or every second day. No objective tumor regression was observed. Six out of 8 patients with carcinoids of the ileum and the caecum showed stable disease lasting for a median of 25 months (range 4-57). In 3 out of 6 patients with carcinoids of rectum, lung and of unknown primary site, stable disease was observed lasting for 2-7 months. The remaining patients had progressive disease. Six out of 9 evaluable patients had a more than 50% reduction of urinary 24 h 5-hydroxyindoleacetic acid excretion lasting for a median of 4 months (range 2-11). Decrease of flushing was noticed in 3 out of 6 evaluable patients and decrease of diarrhea in 5 out of 9 evaluable patients. In 4 patients dose reduction was necessary due to confusion and fatigue.