Abstract: In accordance with the invention, the effect of certain agricultural chemicals, viz. fungicides, herbicides, insecticides, nematocides and plant-growth regulators, is improved by co-administration of them with one or more of the following additives: carbohydrates, organic acids (particularly fatty acids and acids of the Krebs tricarboxylic acid cycle), vitamins and co-enzymes, purine and pyrimidine nucleosides and nucleotides, naturally occurring fats and oils, certain amino acids and (but not when the agricultural chemical is itself a plant-growth regulator) plant-growth regulators. The invention provides compositions containing one or more of the said agricultural chemicals and one or more of the said additives, and methods of improving the harvest of a given crop by applying to it one or more of the said agricultural chemicals and one or more of the said additives, either simultaneously or within up to about ten days of one another.