Not available – first paragraph follows: Isolation of mutants tolerant or resistant to herbicides may become a valuable application of cell culture techniques. Every herbicide is restricted in use by the number of crops it damages or kills. Tolerant mutants of various plant species could broaden the usefulness of currently available herbicides. The advantages of searching for this kind of mutant using cell cultures are (1) accuracy and uniformity of herbicide exposure in culture, (2) the ease with which billions of cultured cells may be screened for ability to grow in the presence of the herbicide, and (3) the potential (as yet unrealized for most crop species) for easy isolation of recessive mutants using haploid cell cultures.