INTRODUCTION: Resistance training has been well established as an effective treatment strategy to increase skeletal muscle mass and strength in the elderly. We assessed whether dietary protein supplementation can further augment the adaptive response to prolonged resistance type exercise training in healthy, elderly men and women. METHODS: Healthy, elderly men (n=31; 70+/-1y) and women (n=29: 70+/-1y) were randomly assigned to a progressive, 24-wk resistance type exercise training program with or without additional protein supplementation (15 g/d). Muscle hypertrophy was assessed on a whole-body (DXA), limb (CT), and muscle fiber (biopsy) level. Strength was assessed regularly by one-repetition maximum (1RM) strength testing. Functional capacity was assessed with a sit-to-stand and handgrip test. RESULTS: 1RM strength increased by 45+/-6 vs 40+/-3% (women) and 41+/-4 vs 44+/-3% (men) in the placebo vs protein group, respectively (P<0.001), with no differences between groups. Leg muscle mass (women: 4+/-1 vs 3+/-1%, men: 3+/-1 vs 3+/-1%) and quadriceps cross-sectional area (women: 9+/-1 vs 9+/-1%, men: 9+/-1 vs 10+/-1%) increased similarly in the placebo vs protein groups (P<0.001). Type II muscle fiber size increased over time in both placebo and protein groups (25+/-13 vs 30+/-9 and 23+/-12 vs 22+/-10% in the women and men, respectively). Sit-to-stand improved by 18+/-2 and 19+/-2% in women and men, respectively (P<0.001). CONCLUSION: Prolonged resistance type exercise training increases skeletal muscle mass and strength, augments functional capacity, improves glycemia and lipidemia, and reduces blood pressure in healthy elderly men and women. Additional protein supplementation (15 g/d) does not further increase muscle mass, strength, and/or functional capacity.