Perineal compression during bicycling appears to be responsible for some cases of erectile dysfunction. In 46 healthy athletic men transcutaneous penile oxygen pressure (tpO(2)) at the glands of the penis was measured, using a transcutaneous measurement device. It has been shown that the tpO(2) levels measured at the glans correlate with the penile blood flow. Our measurements were performed before, during and after cycling in an upright and a reclining position in a crossover study. The mean transcutaneous pO(2) at the glans in a standing position before biking was 60.5+/-8.1 mm Hg. It decreased after sitting on the saddle in an upright position to 17.9+/-3.9 mm Hg. Continued cycling in a seated upright position showed pO(2) levels of 18.3+/-5.2 mm Hg, with a full return to normal pO(2) values after a 10-min recovery period in a standing position. Cycling in a reclining position resulted in pO(2) levels of 59.4+/-4.2 mm Hg, a similar level to that obtained before exercising. The results of the present study demonstrated that there is a deficiency in penile perfusion caused by perineal arterial compression. Cycling in a reclining position - in which no perineal compression was seen - caused no alteration in penile blood flow during exercising. Therefore, we suggest cycling in a reclining position to avoid health hazards - such as penile numbness and hypoxygenation of the corpora cavernosa, which can result in impotency.