Detection of anaerobic threshold (AT) requires either invasive techniques or expensive gas analyzers and somewhat complicated procedures. The purpose of this study was to determine if ventilatory frequency (f) could be used to detect AT. Thirteen (seven females) healthy, non-smoking, physically active adults (21-44 years) volunteered to perform progressive cycle exercise. A protocol of either 22.5- or 45-W increments every 2 min was used according to the subject's weight and fitness to assure steady state. Expiratory gas was measured using a computerized breath-by-breath system. Mean values of oxygen uptake (VO2, 1.min-1), ventilation (VE, 1.min-1), and f(br.min-1) were calculated each min. Peak VO2 ranged from 24.8 to 58.9 ml.kg-1.min with a group mean (+/- SD) of 45.1 +/- 11.6 ml.kg-1.min. Mean (+/- SD) VO2 at AT, as determined by disproportionate increase of VE, was 2.11 +/- 0.57 1.min-1. Mean (+/- SD) VO2 at the point of disproportionate increase of f was 2.09 +/- 0.58 1.min-1. A significant (P less than 0.05) correlation (r = 0.834) was found between the point of disproportionate increase in f and that of VE for individual data. A Student's t test indicated there was no significant difference in mean VO2 at AT. It was concluded that AT could be detected by f in healthy, physically active adults, thus providing a simplified and less expensive alternative method. This finding may have implications with regard to establishing and monitoring exercise intensity.