Intraperitoneal immunization with Freund's adjuvant is frequently used to stimulate antibody production in mice. To evaluate the clinical and pathological effects of this technique, mice were immunized intraperitoneally with complete Freund's adjuvant and albumin, and the injection repeated 3-4 weeks later using incomplete Freund's adjuvant. This regimen induced a mean antibody titer against albumin of 1:280 within 7 days after booster immunization and increased the abdominal width, abdominal circumference and spleen weights of immunized animals. Food intake and body weight decreased after immunization, but returned to control levels within 1-2 weeks. Open-field activity was not affected. Neutrophilia, eosinophilia and monocytosis were present 7 days after immunization and persisted for the duration of the study. Gross and histopathological lesions included multiple granulomatous abdominal adhesions and lymphoid hyperplasia. Thus, intraperitoneal immunization with Freund's adjuvant and albumin produced some adverse effects in the animal (weight loss, neutrophilia and granulomatous peritonitis). However, the animals did not appear to be severely or chronically impaired, since food intake, body weight and locomotor activity were within normal limits for most of the post-immunization period.