The aim of this study was to compare the validity of four physical work and performance tests on bicycle ergometers commonly used in Sweden. The following four tests were compared: a) a work test of submaximal character designed for estimation of the maximal oxygen uptake of the individual (Vo2 max); b) a work test of maximal character designed for estimation of the highest work load an individual can sustain for 6 minutes (Wmax6min); c) the Cycling Strength and Endurance Test (CSET)-a performance test of maximal character consisting of a series of intermittently determined terminal thresholds; and d) a flexible work test of maximal character, the Individually Adapted Work Test (the IA-test): by a feedback mechanism the highest work load an individual can be expected to sustain for 4 minutes is determined. Criteria were cross-country runs (altogether 4) arranged a short time before and after the tests on the bicycle ergometer. Subjects were military conscripts, aged 17-25. When comparisons were made between the best prediction variable of each test, no significant differences were obtained. The size of the validity coefficients was .55-.70. However, the maximal work tests showed the highest validity coefficients. The investigation indicates that, when a work test is to be chosen, the problem, the practical conditions and the resources available should guide this choice.