1. Viruses such as baculovirus can be concentrated by polyethylene glycol precipitation.

2. Adjust the pH of the virus-containing supernatant to 7.2-7.5. Polyethylene glycol (PEG, MW 6,000) is added to a final concentration of 8% (w/v).

3. Stir at 4 °C for 2 hours.

4. Centrifuge at 10,000 x g for 2 hours.

5. Resuspend the pellet in a small volume of appropriate buffer ( e.g., RNase-free ddH₂ for virus RNA prep).