Summary. In male mice which normally do not synthesize measurable amounts of the pregnancy-associated murine protein-1 (PAMP-1), synthesis occurred when there was continuous infusion of hGH but not by repeated subcutaneous injections. The decrease in PAMP-1 values after hypophysectomy in female mice was rapidly restored by continuous infusion of hGH, 80 μg daily. PAMP-1 has generally been regarded as an 'oestrogen-inducible' protein regulated by the oestrogen/androgen balance. Our results suggest that the apparent effects of sex steroids are mediated via the pituitary and possibly growth hormone secretion.