Two-year-old Stanley plum trees were sprayed with solution of potassium salt of alphanaphtaleneacetic acid (NAA). The treatment was repeated at two dates on two groups of trees. The first treatment was conducted by the end of the blooming period after the flowers were fertilized; the second treatment took place 10 days later. The concentrations of NAA varied from 30-80 mg dmˉ³. The percentage of fruit setting, total yield, weight of fruit and extract content were evaluated. Little effects of the applied NAA concentrations on the percentage fruit setting or the total yield were recorded. A higher average weight of fruit was noted in the case of higher concentrations of auxin applied at the first treatment date. A slight effect of the auxin was also recorded in the extract content in fruit.