Upper genital tract infection was investigated in 45 women admitted to hospital for suspected acute pelvic inflammatory disease (PID). Salpingitis was diagnosed by laparoscopy in 30 (67%) women. Histopathological evidence of endometritis was found significantly more often in the 30 women with salpingitis (87%) than in the other 15 women without salpingitis (33%). C. trachomatis or N. gonorrhoeae, or both, were isolated from the upper genital tract in 14 of the 31 women who had both salpingitis and endometritis or endometritis only but in none of the four women who had salpingitis alone and in none of the 10 women who had no evidence of PID. Bacterial vaginosis was associated with histopathological evidence of upper tract infection. Non-chlamydial non-gonococcal organisms were frequently isolated from the upper genital tract. No organisms were isolated from the upper genital tract from 9 of 35 women with laparoscopic or histopathological evidence of PID compared with 7 of 10 women without evidence of PID. C. trachomatis or N. gonorrhoeae in the endometrium was associated with lymphoid follicles comprising transformed lymphocytes, and correlated with the density of plasma cells on biopsy. The microbiological results support the recommendations of broad spectrum antimicrobial therapy for PID.