Mutants resistant to chemicals that inhibit growth (antimetabolites) are the most readily selected in plant cell cultures. A number of such mutants have been isolated, with resistance to amino acids and their analogs, base analogs, toxins from pathogenic microorganisms, herbicides, salts, and antibiotics. The mutants can be used for fundamental investigations into cellular metabolism, as markers for plant genetic manipulation, and in efforts to improve crop tolerance to diseases and agrochemicals. Progress in mutant selection has been reviewed extensively in recent years (1-4). Detailed considerations of the technical aspects of in vitro selection are available (1), and some protocols have been published (4-7).