Cytoplasmic RNAs were prepared by guanidinium thiocyanate-phenol-chloroform method and compared among 3 mouse tissues. The RNA yield was 749㎍, 369㎍, and 60㎍ per g of tissue in liver, spleen, and brain, respectively. When the cytoplasmic RNAs were electrophoresed on composite gel containing 2.2M formaldehyde as denaturing agent, the total numbers of RNA bands were 13, 10, and 11 in liver, spleen, and brain, respectively. The molecular weight of RNAs was ranged from 10,000 to 1,450,000, which was similar but not identical in the 3 tissues tested. When polysomal RNAs were prepared, the yields were 200㎍, 197㎍, and 18㎍, per g of liver, spleen, and brain tissue, respectively. The numbers of polysomal RNA bands were 22, 8, and 13 in liver, spleen, and brain, respectively. The yields of nuclear RNAs were 619㎍, 4090㎍, and 250㎍ per g of liver, spleen, and brain tissue, respectively. The numbers of nuclear RNA bands were 9, 8, and 11 in liver, spleen, and brain, respectively. The RNA band patterns from 3 fractions on the composite gel electrophoresis were not identical in those tissues tested.