The present invention relates to azolin-2-yl-amino compounds of formulae (I. a) and (1.b) and their salts which are useful for combating animal pest, in particular arthropod and nematodes. The present invention also relates to a method for combating such pests and for protecting crops against infestation or infection by such pests. Furthermore, the present invention relates to veterinary compositions for combating animal pests. Formula (I.a), formula (I.b) wherein n is 0 to 4; X is S, O or NR5; A is —C(R6a)(R6b)—, O, NR7, S, S(O) or S(O)2; B is a bond Or CH2; R1 is H, CN, C1-C6-alkyl, C2-C6-alkenyl, C1-C6-alkylcarbonyl, C3-C6-cycloalkyl, phenyl, benzyl, etc.; R2a, R2b are H, CN, C1-C6-alkyl, C2-C6-alkenyl, C1-C6-alkylcarbonyl, (C1-C6-alkyl)-thiocarbonyl, C(O)NRaRb, C(S)NRaRb, (SO2)NRaRb, phenyl, benzyl, 5 or 6 membered heterocyclic ring etc.; or R1 together with R2a is C3-C5-alkandiyl; or R1 together with R2 are C(O); R3a, R3b, R3c, R3d are H, halogen, CN, C1-C6-alkyl, C1-C6-alkylamino, C3-C6-cycloalkyl, phenyl, benzyl, etc.; R4a, R4b are H, halogen, C1-C6-alkyl, C2-C6-alkenyl, phenyl, benzyl, 5 or 6 membered hetaryl; or R4a together with Rb may also be ═O, ═NRC or ═CRdRe; or R2a together with R4a may form a bridging bivalent radical.