Thirty herbicides or plant growth regulators were tested against the pea aphid, Acyrthosiphon pisum (Harris), on broad bean, Vicia faba L. When amitrole at 300, 200 and 100 p.p.m. of active ingredient in water was absorbed by the roots, fecundity of the adults was reduced and mortality of their progeny was 100, 100 and 93.9 per cent respectively. No significant effects on fecundity occurred when amitrole was applied to the leaves or as a contact spray on adult aphids. When Zytron at 3,000, 2,000 and 1,000 p.p.m. of active ingredient in water was absorbed by the roots, mortality of adults was 100, 100 and 95 per cent and of their progeny 100, 100 and 98.6 per cent respectively. When Zytron was applied to the leaves at 8,000, 4,000 and 2,000 p.p.m. of active ingredient in water there was a mortality of adults of 85, 70 and 50 per cent and of nymphs 75.1, 45.4 and 29.9 per cent. The lower mortality of nymphs occurred over a 5-day period, indicating that the initial toxic effects from application to the leaves were soon lost. Mortality of nymphs refers to young aphids born alive and killed by the toxic effects of amitrole or Zytron. Twenty-seven of the chemicals showed no effects on aphids caged on treated plants.