Abstract: The applicability of Cooper equation to the cycloheximide bioassay has been experimentally verified. Then from the theoretical equations previously derived for cupplate and paper-disc agar diffusion bioassay critical concentrations and critical times for cycloheximide evaluated, and finally the calculated results of the theoretical equations and the Cooper equation compared. The results are quite similar. Hence the theoretical equations may provide the theoretical basis for the Cooper equation, and the latter in turn may be regarded as the simplified form of the theoretical equations.