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Three experiments tested modifications of the purine assay designed to improve estimation of microbial crude protein supply. In Experiment 1, changing hydrolysis conditions from 12 normal perchloric acid to 2 normal increased purine recovery and lowered the coefficient of variation. In Experiment 2, phosphate buffer yielded greater recovery of purines than acetate buffer and using the extraction solution as a wash was less variable than silver nitrate in .005 molar hydrochloric acid. In Experiment 3, purine nitrogen:total microbial nitrogen ratios for five forages were determined by incubating NDF in situ and analyzing them before and after neutral detergent extraction.