We have reported (JCEM 60:910,1985) that testosterone increases serum IGF-I levels. To expand our knowledge of the regulation by androgens of other components of the GH-IGFBPs axis we measured serum levels of testosterone, IGF-I, IGF-II AND IGFBPs in 10 prepubertal patients prior to and 7 days after IM testoterone propionate. The patients had been subjected to tests to rule out androgen insensivity; samples only from those with normal responses were selected. IGF-I and II were measured by RIA; IGFBP3 by Western Ligand Blot(WLB); IGFBP3 by IRMA (DSL). After IM testosterone serum IGF-I, IGF-II, IGFBP3 and the IGF-I/IGFBP3 molar ratio increased significantly = 138.3 ± 31.6 vs 277.6 ± 47.2, p<0.001; 747.2 ± 81.9 vs 951.0 ± 85.2, p<0.05; 2.73 ± 0.24 vs 3.15 ± 0.20, p<0.05; 0.179± 0.028 vs 0.326 ± 0.057, p<0.01 respectively (Mean + SEM, ng/ml, ng/ml, μg/ml, paired t test). WLB did not show significant changes in the IGFBPs. Our results show thad test-osterone is able to increase not only IGF-1 serum levels, but also IGF-II and IGFBP3. We thus include androgens as modulators of the serum levels of these components of the GH-IGFs-IGFBPs axis. The IGF-I increment, proportionally greater than the IGFBP3 increase, induced an 82% elevation of the IGF-I/IGFBP3 moler ratio, pointing out an increase in free IGF-I, favouring testosterone induced growth.