Abstract: Regeneration and separation of catalysts Me(CO)(PR.sub.3).sub.2 Hal(I) and HMe(CO)(PR.sub.3).sub.3 (II), where Me is rhodium or iridium, Hal is halogen and R denotes the same or different hydrocarbon radicals, from distillation residues of hydroformylation mixtures by treating said residues with aqueous acids and peroxides, mixing the resulting Me salt solutions with water-soluble organic solvents and with a phosphine PR.sub.3 and, in the case of the preparation of compound I, with a hydrohalic acid or an alkali metal halide, reacting the solutions at from 0.degree. to 150.degree. C. and from 1 to 250 bars in case I with carbon monoxide or compounds eliminating carbon monoxide and in case II additionally with hydrogen, and separating the resulting compound I or II.