Guinea pigs were immunized with autologous serum exposed to chlorhexidine gluconate. Injections were given every second day for one week. After four weeks the animals were given a booster-dose and were tested for antibodies using the cutaneous anaphylaxis test. The titre of chlorhexidine-treated serum showing a positive reaction was 1: 1000 in immunized animals. Control animals showed positive reaction in a dilution of 1: 10 but negative in 1: 100.