AbstractThe potential of plant cell suspension cultures for the biotechnological production of high‐cost, plant‐specific compounds is critically evaluated. The basic roles of nutrient media and phytohormones are described followed by a description of the recent progress in mass cultivation of plant cell cultures as measured by biomass and doubling time. The accumulation of secondary constituents in cell cultures is reviewed and methods for the selection of high‐producing strains are described. The essential features of the selection strategy are the establishment of cell cultures from high‐producing plants and a sensitive assay (e.g. radio‐immunoassay) for the screening of microcolonies grown on petri dishes.The accumulation of biosynthetic intermediates of secondary constituents in cell culture strains will possibly lead to the isolation of novel compounds. Similarly, the appearance of different pattern of secondary compounds in plants and their derived cell cultures will make screening of cell cultures with pharmaceutically oriented bioassays a worthwhile procedure. Considerable emphasis has been placed on biotransformation reactions of various steroids and particularly the 12‐β‐hydroxylation of cardiac glycosides. The present status of the latter reactions as carried out by selected strains ofDigitales lanatain fermenter systems with β‐methyldigitoxin is described. Studies of the position‐specific glucosylation of 6,7‐dihydroxycoumarin to esculin are presented and competitive side reactions of phenolic substrates described. The growth‐phase dependent expression of enzymic reactions in cell cultures is exemplified by recent studies on an acylglucoside transferase.Finally, the new methodology of immobilized cells has recently been applied to plant cell cultures. Preliminary results on anthraquinone and alkaloid biosynthesis as well as biotransformation