Experiments were performed to ob serve the in f lu ence of X-raj irradiation on mast ce ll s and mastoca lcergy in ïat s.Anima ls were irradiated sing l e dose of X-ray . X-ray irradiation was app lied to the who le body in doses eith er 100 rads or 15 0 rads(Cobalt-60 Teleth eraphy Unit) . O ne day after irradiation th e.rats we re injected lead acetate intravenously , followed by injection of compound 48/80 in the ba ck subcutaneously Animals were kil led by decapitation at intervals, 1 hour, 5 hours , 1 day and 6 da ys after subcutaneous in)cction.Specímens of the abdominal and ba ck sk in were f ixe d in al coh olformol solution and stained with th e fo Jl owing methods; H -E for observation of pathological changes of ti ssues, toluidin e blue for demonstration of mast cells, vo n Kossa-azure A for demonstration of carbonate and pho sphate , and chloran il ic acid for demonstration of calcium.The f ollowing co nclusions were obtained .Cal ciph ylatic wheals ar e large size in the control group , m edium size in 100 rads ir radiation group and sma Jl size i n 150 rads i .. radiation group In X-ray irradiaion groups the number of mast cell s decreases more in t h e 150 rads tha n in t he 100 rads irrad iation.In the 100 rad s X-ray irradiatio n group , histochemical study of the injection sites showed that calcium impreg nated t o mast ce ll granules an d co nn ecti ve tissue fibers in 1 day s after su bcu ta neous injection.The morphogenesis of this calcinosis was t h e same in the ra t of 5 hours after su bcu taneous injection of the co ntrol group . Whereas , 1 day after subcutaneous inection in 150 rad s X-ray irradiation group cal cium deposited more slightly than other gro ups.