Abstract The importance of six theoretically calculated molecular parameters in the antigibberellin (retardant) activity of quaternary ammonium salts is studied using a regression analysis. A bioassay system based on cell culture of fungus Gibberella fujikuroi is used to determine the activity. In the case of N, N, N-trimethyl-N-(2-hydroxyethyl) ammonium chloride (choline) and N, N, N-triethyl-N-(2-hydroxyethyl) ammonium chloride (N, N, N- ...