WEANLING rats tolerated skin homografts longer, Fisher et al.1reported, if made deficient in pyridoxine (vitamin B6); but human volunteers did not when made acutely deficient.2In the present study, begun before Fisher's study with humans, some dogs tolerated homografts longer if made chronically deficient. Methods All dogs were small, healthy, adult, mongrel males. Before the experiment they received a vermifuge and 2 injections of hyperimmune serum. Studies including body weights, complete blood counts, and total and fractional serum protein concentrations were obtained before the diet, before grafting, and about 12 days after grafting in most instances. In addition, in 10 control dogs serum protein concentrations were obtained on the 7th, 10th, 12th, and 14th days after grafting. Serum fractionation was done in duplicate with Spinco electrophoresis apparatus by Method A and B, Spinco Manuals R 1M5 and 01R-1. If a serum sample had visible hemolysis, indicating