1. Warm plates to room temperature before use. Cold plates causes the top agar to solidify irregularly. DO not warm plates to 37° as the top agar will take forever to solidify. - Prepare top agar as the appropriate liquid medium with 0.7% agar. Keeping 100 mL bottles is convenient. For phages, use λ top agar, which is less rich and yields bigger plaques. - Melt top agar in the microwave completely. Allow the agar to boil after liquification; incompletely melted agar looks liquid, but is grainy. - Allow agar to cool to 48°. Store in the 48° waterbath for convenience; old agar turns dark and should be discarded. Agar with drugs cannot be stored. - Add cells and phage to a 13 mm yellow-capped tube in the 48° temperature block. - Remove the cap and add 2.5 mL molten top agar. Do not replace cap. - Immediately vortex the mixture, flame the top, and dispense the mixture onto the appropriate plate. Swirl the plate to evenly distribute the agar. - Allow the plate to stand for several minutes as the agar cools. - After the top agar is solid, invert plate and incubate.