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Three varieties and two hybrids of grain sorghum were sprayed with atrazine at the rate of 2.7 kg a.i./ha (2.4 lb a.i./A). A single treatment was given to each plot and applications were made at weekly intervals, beginning 1 week after emergence. Pollen mother cells collected from each genotype treated at seven developmental stages were examined. Many affected microsporocytes were observed. Abnormalities consisted of multinucleate cells, bridges, and increased chromosome numbers, some of which were not a multiple of the basic number. Dyads and quartets often contained micronuclei. Atrazine treatment apparently interfered with meiotic stability regardless of time of application. Statistical analyses of grain yield, head weight, kernel weight, fertility, stalk diameter, and germination percentage indicated that treated groups did not differ from the control group. Plant height, however, differed between control and treated groups. No consistent relationship was observed between content of protein, soluble and total carbohydrates, and date of treatment. Also, no apparent relationship existed between frequency of chromosomal aberrations and agronomic responses following atrazine application.