Adriamycin is an antibiotics of the anthracycline group which strongly inhibits a variety of transplantable tumors. It is currently being used for the treatment of human cancer. Treatment of the cultured L5178Y cells with 0.1㎍/㎖ adriamycin for 4hrs, which led to 80∼85% cell kill, inhibited only slightly and to the same extent (10∼20%) the synthesis of DNA, RNA and protein. The results suggested that cell death was not caused primarily by the inhibition of DNA synthesis in L5178Y cells. Studies of the effect of adriamycin on various RNA species showed that the synthesis of ribosomal RNA was more susceptible to inhibition by the drug than messenger RNA or heterogeneous nuclear RNA. The synthesis of small cytoplasmic RNA species, including transfer RNA, was not significantly inhibited under the condition which resulted in almost complete inhibition of ribosomal RNA synthesis.