This investigation determined the influence of acute and chronic resistance exercise on responses of growth hormone (GH) molecular variants in women. Seventy-four healthy, young women (23±3y, 167±7cm, 63.8±9.3kg, 26.3±4.0% body fat) performed an acute bout of resistance exercise (6 sets of 10 repetition maximum squat). Blood samples were obtained pre- and post-exercise. Resulting plasma was fractionated by molecular weight (A: >60 kD; B: 30-60 kD, and C: <30 kD) using chromatography. Fractionated and unfractionated (UF) plasma was then assayed for GH using 3 different detection systems (monoclonal immunoassay, polyclonal immunoassay, and rat tibial line in vivo bioassay). Subjects were then matched and randomly placed into one of four resistance exercise training groups or a control group for 24-wks. All experimental procedures were repeated upon completion of the 24-wk resistance training programs. Following acute exercise, immunoassays showed consistent increases in UF GH samples and B and C fractions; increases in A fractions using immunoassay were seen only in the monoclonal assay. No consistent changes in bioactive GH were found following acute exercise. Conversely, chronic exercise induced no consistent changes in immunoassayble GH of various molecular weights, while, in general, bioassayable GH increased. In summary, although acute exercise increased only immunoactive GH, chronic physical training increased the biological activity of circulating GH molecular variants. Increased bioactive GH was observed across all fractions and training regimens, suggesting that chronic resistance exercise increased a spectrum of GH molecules which may be necessary for the multitude of somatogenic and metabolic actions of GH.