Acid phosphatase (EC 3. 1. 3. 2) activity was measured in sunflower (Helianthus annus L.) cotyledons. The present results indicate that the tested growth regulators indoleacetic acid (IAA), naphthylacetic acid (NAA) and indolephenoxyacetic acid (IPA) induced acid phosphatase activity at concentration range 100-400 µM. The enzyme was inhibited by CdCl₂ and PbCl₂ at 20-100 µM. Cd²⁺ and Pb²⁺ enhanced lipid peroxidation and H₂O₂ content. Malondialdehyde (MDA) content was reduced in cotyledons pretreated with GA₃. Salinity induced lipid peroxidation and increased H₂O₂ content. NaCl at low concentrations (50 and 100 mM) induced the enzyme activity whereas the higher concentrations (150-300 mM) reduced the activity. Coronatine (COR) at 100 µM alleviated partially the toxic effect of salinity.