Currently, the recommended dietary allowance for protein determined for sedentary individuals is assumed to be adequate for athletes. However, several types of evidence (in vitro, in situ, and in vivo) indicate that exercise causes substantial changes in protein metabolism. In fact, recent data suggest the protein recommended dietary allowance may actually be 50 to 100% higher for individuals who exercise on a regular basis. Optimal intakes, although unknown, may even be higher, especially for individuals attempting to increase muscle mass and strength. The reasons why the recent experimental results contradict older studies are complex and not fully understood. However, dietary (total energy input, percent of each foodstuff, accommodation to treatments), exercise (type, frequency, intensity, duration, training, environment), and methodological (in vitro, in situ, in vivo) considerations are likely very important. This paper reviews the recent findings and discusses their implications to exercise performance. Although, definitive recommendations regarding optimal protein intakes for various athletic groups are not yet possible, it appears that exercise increases protein needs. It is hoped that well-controlled studies will be completed in the near future so that such recommendations will soon be possible.