According to their susceptibilities to antihistamines, diethylcarbamazine, and colchicine, 6 types of cutaneous anaphylaxis in the rat were characterized. (1) The ACA reaction was highly sensitive to antihistamines and diethylcarbamazine but almost insensitive to colchicine. (2) The homologous PCA reaction by the ‘early’ antibody was almost completely inhibited by antihistamines but little affected by colchicine. This reaction was also significantly suppressed by diethylcarbamazine. (3) When sensitization was made with the intradermal injection of the homologous hyperimmune antiserum, the PCA reaction was insensitive to any of antihistamines, colchicine, and diethylcarbamazine. (4) When local sensitization was made using the heterologous antiserum, the PCA reaction was depressed by colchicine but not by antihistamines or diethylcarbamazine. (5) When the rats were generally sensitized by the intravenous injection of the homologous hyperimmune antiserum, the PCA reaction was quite sensitive to antihistamines and diethylcarbamazine but not to colchicine. (6) When systemic sensitization was made using the heterologous antiserum, the PCA reaction was highly sensitive to both of antihistamines and colchicine.