The results of penile tumescence recordings from first- and second-night polysomnograms from 146 normal subjects are presented for four age groups. The data are in close agreement with basic tumescence parameters that have been presented earlier. In addition, results from first and second nights are compared, and data are presented from base and coronal sulcus (tip) recordings locations. The results indicate that tumescence parameters that are most correlated with rapid-eye-movement sleep are those most likely to significantly differ from the first to the second night. Base and tip recordings closely paralleled each other. Additionally, tumescence periods were also divided into three phases that are likely to correspond to different physiological states. These three phases, Tup, Tmax, and Tdown, vary in their sensitivity to night and age effects. It is hypothesized that changes in different tumescence phases may reflect different pathophysiologies.