This chapter describes a protocol modification of the bacterial reverse mutation test (Ames test). It is based on the same principle as the Ames test in Petri dishes, but uses a liquid, low volume microplate version of the fluctuation method. Clear strengths are the low compound requirement, and the increased throughput as compared to the traditional format in Petri dishes. The liquid system allows for processing several replicates at once with the possibility of using pipetting robots and has an easy colorimetric read-out instead of counting revertant colonies. The Ames II and MPF™ also use less S9 and produce less hazardous waste due to the low volume multi-well format.