Of the total number of dogs with complications following ovario-hysterectomy submitted during the period from January 1977 to July 1979 (109), fifty-five showed gynaecological symptoms such as discharge of the vulva (28), attractiveness to male dogs (37), periods of heat (28) and pseudopregnancy (14). In addition to a general clinical examination, the dogs (forty-two of these fifty-five weighing more than 20 kg) underwent a selective gynaecological examination usually consisting in clinical, cytological and bacteriological studies and estimation of the progesterone level of the peripheral blood. At the same time, the progesterone levels of the peripheral blood of six beagles were studied for comparative purposes during pro-oestrus, oestrus and metoestrus; the maximum progesterone level was recorded about day 20 and varied from 35 to 60 ng/ml. The average progesterone level was determined in thirty-nine beagles during anoestrus and found to be 0.24 +/- 0.02 SEM ng/ml. The basal progesterone level was determined in eight dogs in which total ovariohysterectomy had been performed (0.14 +/- 0.02 SEM ng of progesterone /ml). When a cytological study was done in the dogs with residual ovarian tissue, an oestrus pattern was observed in 39 per cent of the cases, the progesterone level of the peripheral blood being above the basal level in 70 per cent of the cases. Remnants of ovarian tissue were removed during laparotomy in forty-seven dogs, on the right side in forty-one cases and on the left in twenty-two cases. The uterocervical stump was shortened when uterine tissue was probably or obviously present. The uterine stump was more or less severely inflamed in nineteen cases. The procedure was confined to shortening of the uterocervical stump in eight dogs in which ovarian tissue was not found to be present. The inflamed stump contained an unabsorbable ligature in seven dogs, the uterocervical stump of the eighth dog not being examined.