A protocol is presented for the simultaneous isolation of DNA and RNA from giant-celled green algae. The overall quality of the DNA was examined by the A(260)/A(280) ratio, agarose get electrophoresis, and restriction enzyme analysis. Denaturing gel electrophoresis and cDNA cloning were used to investigate the quality of the RNA. These assays indicated that both the DNA and RNA isolated by this procedure are of high quality, suitable for further molecular analyses. Since many of these algae are slow growing and therefore only a few grams may be available, the isolation of DNA and RNA from the same plant material has obvious advantages.