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Summary. Oestrus, expected to be followed by a short luteal phase, was induced in post-partum cows by weaning their calves at 35 days after parturition. Ovaries containing the first preovulatory follicles (Type F) formed after parturition were collected 3 h after the onset of oestrus. For comparison, preovulatory follicles (Type C) were collected 3 h after the onset of oestrus in normally cycling cows. The number of granulosa cells was determined and the concentrations of receptors for follicle-stimulating hormone (FSH) and luteinizing hormone (LH) in granulosa cells and for LH in theca cells were measured. Concentrations of oestradiol-17β, testosterone, androstenedione and progesterone in follicular fluid were also measured. Type F follicles contained about twice the number of granulosa cells (based on DNA) as did Type C follicles (45·8 ± 11·3 and 24·5 ± 3·9 μg DNA/follicle, respectively; P …