['To determine the effect of repeated freezing and thawing, and storage temperature, on the assay results of commonly measured reproductive hormones, and sex hormone-binding globulin (SHBG) in human serum.', 'Prospective laboratory study.', 'Academic medical center.', 'Four men and three pregnant women in the third trimester.', 'Pooled serum from men and pregnant females were frozen at either -20 degrees C or -70 degrees C. Aliquots were then subjected to repeat freeze/thaw cycles, from 1 to 10 times, and assays were performed after the final freeze/thaw cycle.', 'Assay results for eight hormones (FSH, LH, PRL, androstenedione (A), 17alpha-hydroxyprogesterone, P, insulin, and SHBG, as a function of the number of freeze/thaw cycles and storage temperature.', 'Only SHBG in male serum at -20 degrees C and P in pregnant serum at -70 degrees C showed statistically significant decreases in assay results with repeated freeze/thaw cycles (3.3% and 1.1% per cycle, respectively). All other analytes did not show significant changes as a function of freeze/thaw cycles or storage temperature.'] Does repeated freezing and thawing generally alter assay results for several commonly studied reproductive hormones?