A method for extracting nucleic acids from a biological sample by isolating nucleic acid-containing particles from the biological sample by one or more centrifugation procedures, performing one or more steps to mitigate adverse factors that prevent or might prevent high quality nucleic acid extraction, and extracting nucleic acids from the isolated particles. The centrifugation procedures are performed at a speed not exceeding about 200,000 g. The extracted nucleic acids contain both 18S and 28S rRNA.