Hydrazono-malonitrile derivatives of the formula (I) in which R.sup.1, R.sup.2, R.sup.3, R.sup.3' and R.sup.4 have the meanings given in Claim 1 act as phosphodiesterase IV inhibitors and can be employed for the treatment of osteoporosis, tumours, cachexia, atherosclerosis, rheumatoid arthritis, multiple sclerosis, diabetes mellitus, inflammatory processes, allergies, asthma, autoimmune diseases, myocardial diseases and AIDS ##STR00001##