The dirty picture. Quite often, specimens are not purified in any way and investigators examine crude lysates. This is almost certain to go wrong. Crude lysates contain huge amounts of impurities, notably proteins (Figs. S4 and S19). This results in contrastless, flat images and the presence of bacterial debris and even complete bacteria. The debris may mimic certain types of bacteriophages ( Table 2) . Images of nonpurified specimens should not be accepted for publication. Purification can be achieved by centrifugation in sucrose or CsCl density gradients; unfortunately, this technique is limited to a small number of specialized laboratories. Instead, we recommend to sediment phages in Eppendorf tubes followed by two washes in buffer or even tap water. Using fixed-angle rotors, phages can be sedimented in as little as 1 h at 25,000 g. It is not necessary to stain phages for long minutes or to fix them. Staining is almost instantaneous and fixation is merely a complication. While purification is mandatory for any real investigation, crude lysates can be examined for quick checks of phage presence and identity. It is also possible to examine phages extracted from a lysed agar surface. 23 For this, a drop of staining solution is deposited on the agar and the Petri dish is agitated gently. The drop is then touched with a grid and excess liquid is drawn off.