This chapter describes the different aspects of hypocholesterolemic agents. A sensitive and simple assay of in vitro cholesterol synthesis was described by Kuroda and Endo, in which the labeled precursors are incubated with rat liver enzyme preparations. The synthesized sterols are saponified and extracted with light petroleum. Sterols are isolated from the extracts as digitonide and counted. The rat liver enzyme preparations are stable at −80°C and retain their catalytic activity for at least 4 months, unless freezing and thawing are repeated, which causes a loss in activity. By using this procedure, 50 to 100 culture broths can be tested at a time for their activity to inhibit ...