Maximum oxygen uptake and the running speed at the anaerobic threshold were determined during treadmill running. Performance in these laboratory tests and performance on a squash-specific field test were compared and examined with respect to subjective ratings of squash fitness. The field test was performed in a squash court. Six light bulbs were connected to a programming device causing individual bulbs to light up in a given sequence. The players were instructed to react to the flashes by running towards and striking balloons mounted in the vicinity of the bulbs. By altering the interval between the lighting of the bulbs the intensity of exercise could be varied. The test consisted of a series of 3 min periods of exercise at increasing intensities (increased number of runs per unit of time). The results showed a low correlation (r = 0.52) between treadmill ergometry data and a rank-order list based on an independent, partly subjective estimate of fitness. A higher correlation (r = 0.90) was found for the results of the field test and the rank-order list. Maximum oxygen uptake values and anaerobic threshold values derived from laboratory measurements were thus not sufficient for a valid estimate of competition fitness in these players. The results show that a valid estimate of fitness can be derived from measurements involving exercise closely resembling that which is specific for the sports activity in question. Improved training advice and guidance may result from such studies.