We investigated the response of insulin-like growth factor (IGF- I), insulin-like growth factor binding protein-3 (IGFBP-3) and some hormones, i.e., testosterone (T), growth hormone (GH), cortisol (C), and insulin (I), to maximal exercise in road cyclists with and without diagnosed left ventricular hypertrophy. M-mode and two-dimensional Doppler echocardiography was performed in 30 professional male endurance athletes and a group of 14 healthy untrained subjects using a Hewlett-Packard Image Point HX ultrasound system with standard imaging transducers. Echocardiography and an incremental physical exercise test were performed during the competitive season. Venous blood samples were drawn before and immediately after the maximal cycling exercise test for determination of somatomedin and hormonal concentrations. The basal concentration of IGF-I was statistically higher (p < 0.05) in athletes with left ventricular muscle hypertrophy (LVH) when compared to athletes with a normal upper limit of the left ventricular wall (LVN) (p < 0.05) and to the control group (CG) (p < 0.01). The IGF-I level increased significantly at maximal intensity of incremental exercise in CG (p < 0.01), LVN (p < 0.05) and LVH (p < 0.05) compared to respective values at rest. Long-term endurance training induced an increase in resting (p < 0.01) and post-exercise (p < 0.05) IGF-I/IGFBP-3 ratio in athletes with LVH compared to LVN. The testosterone (T) level was lower in LVH at rest compared to LVN and CG groups (p < 0.05). These results indicate that resting serum IGF-I concentration were higher in trained subjects with LVH compared to athletes without LVH. Serum IGF- I/IGFBP-3 elevation at rest and after exercise might suggest that IGF-I act as a potent stimulant of left ventricular hypertrophy in chronically trained endurance athletes.