A new, rapid, and simple method for the isolation of either RNA or DNA from cerebrospinal fluid samples for subsequent amplification by specific polymerase chain reaction (PCR) assays is described. The technique involves a single extraction with a guanidinium thiocyanate acid (GuSCN) buffer, and does not require the use of organic solvents. Applied to the recovery of enteroviral RNA, herpes simplex virus (HSV) and Varicella-zoster virus (VZV) DNAs the method has proved to be of equivalent or better efficiency than established methods of nucleic acid separation but is less laborious and time consuming. The simplicity of the procedure permits the processing of large numbers of samples and the use of a single preparative method for either RNA or DNA PCR makes it an attractive method for the routine laboratory.