The effects of simazine on shoot culture of two varieties of strawberry were investigated with a view to establishing a system for in vitro selection of resistant mutants. In single shoots some chlorophyll loss occurred at herbicide levels producing little growth inhibition, but efficient bleaching was associated with severe suppression of growth. Varying simazine and sucrose levels, in both single and multiple shoot cultures did not reveal any conditions where chlorophyll destruction and growth inhibition could be separated. A protective effect, against bleaching, of high sucrose levels was not linked to suppression of photosynthesis, as assessed by CO2-fixation measurements. Mutagenesis with nitrosomethyl urea resulted in chlorophyll deficiencies in about 10% of shoots arising from axillary buds, but no resistant sectors emerged from 8000 and 400 mutagenized explants placed on medium containing inhibitory levels of simazine and streptomycin sulphate, respectively.