Resorufin product formation as a result of reagent contact with viable cells is accumulative and proceeds as a function of time. Although somewhat dependent upon cell type, metabolic rate and number per well, 2-4 hr of incubation with the reagent is typically sufficient to generate signal windows for adequate statistical discrimination in HTS. ( Table 1 ) Fluorescent resazurin reductase assay chemistries have been adapted to 1536 well formats, but are typically most useful at lesser plate densities (384 and 96) due to practical limitations associated with prolonged incubation periods [19, 20] .