The aim of the study was to evaluate the in situ degradation kinetics of some commonly used protein sources (sunflower meal, cottonseed meal, and soybean meal). Three ruminally fistulated rams were utilized in the study. They were fed ground alfalfa and a mixture of concentrate (60% alfalfa and 40% mixture) at maintenance level. The Dacron bags used in the study had a 45 p 2, pore size and internal dimensions of 15 x 7 cm. Feed samples were ground to pass through a 2 mm screen. Samples were incubated in the rumen of rams for 0, 2, 4, 8, 12, 24 and 48 h. Each feed sample was incubated in the rumen of 3 rams in duplicate for each incubation time. Approximately 3.5 g of samples were placed in each Dacron bag.