There are provided new 3-hydroxy-4-aryl-5-oxo-pyrazoline derivatives of the formula (I) ##STR1## in which A and B are identical or different and independently of one another in each case represent hydrogen, alkyl, alkenyl, alkynyl, alkoxyalkyl, alkylthioalkyl, cycloalkyl or optionally substituted aryl or A and B together represent the bivalent radical of a saturated or unsaturated, optionally substituted, mono-, bi-, tri- or polycyclic system, X represents alkyl, halogen or alkoxy, Y represents hydrogen, alkyl, halogen, alkoxy or halogenoalkyl, Z represents alkyl, halogen or alkoxy n represents a number 0, 1, 2 or 3, G represents hydrogen (a) or the groups ##STR2## in which E represents a metal ion equivalent or an ammonium ion, L and M represents oxygen and/or sulphur, and R.sup.1, R.sup.2, R.sup.3, R.sup.4, R.sup.5, R.sup.6 and R.sup.7 have the meaning given in the text of the application. The new 3-hydroxy-4-aryl-5-oxo-pyrazoline derivatives of the formula (I) have a particularly pronounced activity against animal pests, in particular against insects and arachnids, and against weeds.