For the removal of turbidities in reaction mixtures clouded by sample material, especially for photometric measurement, there are added to the reaction mixture:(a) at least one low molecular weight organic compound, such as an aromatic alcohol or amine, which contains an electronegative substituent, for example a phenol or naphthol, which is substituted with one or more halogen atoms and/or hydroxyl groups and(b) at least one detergent which dissolves to give without compound (a), a clear solution and which forms a sparingly soluble complex with component (a), such as a non-ionic polyethylene oxide adduct or a cationic detergent, especially an alkyl, aralkyl or alkylthio ether or an alkyl or aralkyl ester of a polyethylene oxide glycol containing 8 to 22 carbon atoms in the alkyl radical and 5 to 25 ethylene oxide units or an alkyl dimethyl benzyl ammonium chloride compound containing 8 to 22 carbon atoms in the alkyl radical,in an amount sufficient for the appearance of a precipitate of the complex, whereafter further detergent is added thereto until the precipitated complex dissolves again.