12 HBsAg-positive patients with chronic active hepatitis B were treated monthly with cell walls (5 or 10 mg) of Propionibacterium granulosum KP-45 (PG) intravenously administered for a period of 6-10 months. The clinical state was evaluated according to an arbitrary 6-grade scale based on serum biochemical tests, HBV markers and the morphology of liver biopsy samples. Intravenous administration of PG was well tolerated, and no serious side effects were observed. All patients exhibited complete or partial normalization of biochemical parameters and HB5AG and DNA-polymerase levels were decreasing after 6 months of therapy. Prior to treatment, HBeAG was detected in 9 patients, in 4 of whom seroconversion occurred with appearance of anti-HBeAg. Excellent results were seen in 3 patients and beneficial results in a further 3 patients; signs of improvement were seen in 5 patients, and only one patient did not react in a clearly positive way. In 11 of these patients, before and during treatment, isolated peripheral blood lymphocytes were investigated for their ability to show rosette E formation, their reactivity to phytomitogens (PHA, ConA), and their suppressor T lymphocyte activity. In five patients interferon levels were investigated.