The direct handling of acrolein for the purpose of combatting microbial, vegetable and animal pests in water and soil is problematic on account of the potential for danger of acrolein. According to the invention a composition which releases acrolein upon contact with water at the site of use and is easy to handle is used. The composition in accordance with the invention contains an acrolein acetal, preferably 2-vinyl-1,3-dioxolane, and a compound hydrolyzable to an acid with a pK.sub.s value of less than 4, especially one from the series of organic acid anhydrides, organic acid halides and inorganic halogen compounds forming hydrogen halide upon hydrolysis.