SOGEN and ISOGEN-LS are homogenous liquids containing phenol and guanidine thiocyanate, with ISOGEN-LS containing more phenol than ISOGEN. ISOGEN is used for the samples of tissues and cultured cells, and ISOGEN-LS is effectively used for samples of large volume such as blood (> 100µl when processed in a 1.5ml plastic tube) and liquid samples that are difficult to concentrate. ISOGEN or ISOGEN-LS is added to a sample, and after dissolving or homogenizing, chloroform is added to the mixture and centrifuged. The homogenate is separated into 3 phases: an aqueous phase, an organic phase and an intermediate phase. In the aqueous phase, only RNA is present, and DNA and protein are present in the intermediate phase and the lower phase. The aqueous phase is collected, and RNA is precipitated by adding isopropanol. DNA is precipitated by adding ethanol to the residual intermediate phase and organic phase, and protein is then precipitated by adding isopropanol. In this way, RNA, DNA and protein can be sequentially isolated.