Objective To evaluate the blood supply to the penis during bicycling and thus determine whether the associated perineal compression might be responsible for some cases of impotence. Subjects and methods The transcutaneous penile oxygen partial pressure (pO2 ) at the glans of the penis was measured in 25 healthy athletic men; pO2 is readily measured by noninvasive techniques currently widely used in the management of premature infants, and which have been shown to give pO2 levels that correlate with arterial pO2 levels. The measurements in the healthy subjects were taken in various positions, before, during and after bicycling. Results The mean (sd) pO2 of the glans when standing before cycling was 61.4 (7.2) mmHg; it decreased after 3 min of cycling to 19.4 (4.7) mmHg. After 1 min of cycling in a standing position it increased significantly to 68 (7.6) mmHg; when cycling was continued in a seated position, after 3 min the pO2 fell to 18.4 (4.2) mmHg and there was a full return to normal pO2 values after a 10‐min recovery period. Conclusion The pO2 seems to correlate with the blood supply to the penis. The present results support the hypothesis that as the penile arteries are compressed against the pubic bone by the saddle during bicycling, the pO2 values decrease. Additionally, shifting from a seated to a standing position while cycling significantly improved the pO2 value of the penis and penile blood oxygenation was then even greater. Therefore, we suggest that cyclists change their body position frequently during cycling. Correcting the handlebars or the height of the saddle, tipping the nose of the saddle to produce a more horizontal, or even downward pointing position, and attention to the design of the saddle may be the only required precautions.