1. Gibberellin (GA), when sprayed on Zinnia elegans, variety Scarlet Flame, was most effective in inducing internodal elongation at a temperature (15.5⚬ C.) below that considered optimum (18.3⚬ C.) for best commercial growth. 2. A combination of low temperatures (10⚬, 12.8⚬ C.) and high GA concentrations (100, 1000, 10,000 p.p.m.) was more effective than one of high temperatures (18.3⚬, 21.1⚬ C.) and high GA concentrations (100, 1000, 10,000 p.p.m.) in inducing internodal elongation. 3. A combination of intermediate temperature (15.5⚬ C.) and low GA concentrations (0.0001, 0.001, 0.01 p.p.m.) was more effective in inducing internodal elongation than one of low temperatures (10⚬, 12.8⚬ C.) and low GA concentrations (0.0001, 0.001, 0.01 p.p.m.), which, in turn, was more effective than one of high temperatures (18.3⚬, 21.1⚬ C.) and low GA concentrations (0.0001, 0.001, 0.01 p.p.m.). 4. Quantitative but not qualitative differences in internodal elongation appeared between plants grown under the 8-hour and 24-hour photoperiods. It would appear that length of photoperiod has only an indirect effect on GA induction of growth.