Factors affecting the characteristics of corpora lutea (number, left/right ovary origin, weight, DNA and progesterone content) were studied in 73 healthy bitches divided into two classes of age (≤2.5 vs. >2.5 years; mean±S.E. = 3.6±0.3 years; range: 0.7–10 years), weight (≤20 vs. >20 kg; mean±S.E. = 16.2±1.2 kg; range: 5–45 kg), reproductive status (pregnancy vs. diestrous; pregnant bitches N= 41 and diestrous bitches N= 32), stage of luteal phase (20–40 vs. 41–55 days) and ovulation rate (≤7 vs. >7). Two different assessments were performed: (a) comparison of luteal tissue characteristics and progesterone content between pregnant and diestrous bitches and (b) investigation of the effect of animal age, weight and ovulation rate on individual corpus luteum (CL) parameters. None of the luteal parameters differed between pregnant and diestrous bitches, even when the stage of the luteal phase was considered. Age and weight of the bitch significantly influenced luteal tissue characteristics: heavier bitches had more and heavier CLs (P