Interpretation of the vectorcardiogram in athletes requires normal values based on quantitatively analyzed data obtained in large groups of athletes. Frank electrocardiograms of extensively trained white athletes aged 23 +/- 5 years were analyzed by computer. Different sport disciplines were included. Tables are provided describing the results for the complete group of 70 athletes (A), respectively indicating the difference between 27 footballers (F) and 16 endurance athletes (E). A critical comparison with two control groups is also discussed, as for other purposes, vectorcardiograms had been collected in healthy non-trained young men, respectively 68 medical students (MS) and 63 nurse students (NS). The following figures may serve as an example to illustrate the difficulty of constituting and using similar normal limits in athletes: mean QRS spatial maximal amplitude (mV.) was respectively 1.82 (MS), 2.03 (NS), 2.17 (A), 1.97 (E), 2.29 (F). It can often be hazardous to attribute certain deviations of electrocardiological measurements to training effects in the athlete.