Abstract: Piperidinyl, pyrrolidinyl, azepinyl and piperazinyl pyridazines of formula ##STR1## wherein one or two carbon atoms of the ##STR2## moiety may be substituted with C.sub.1-4 alkyl, C.sub.1-4 alkyloxy or two carbon atoms of the CH.sub.2 groups of said moiety may be bridged with a C.sub.2-4 alkanediyl radical;X represents CH or N; R.sup.1 represents hydrogen, C.sub.1-4 alkyl, halo, hydroxy, trifluoromethyl, cyano, C.sub.1-4 alkyloxy, C.sub.1-4 alkylthio, C.sub.1-4 alkylsulfinyl, C.sub.1-4 alkylsulfonyl, C.sub.1-4 alkyloxycarbonyl, C.sub.1-4 alkylcarbonyl or aryl; R.sup.2 and R.sup.3 each independently represent hydrogen or C.sub.1-4 alkyl; Alk represents C.sub.1-4 alkanediyl; R.sup.4 and R.sup.5 each independently represent hydrogen, C.sub.1-4 alkyl or halo; andHet represents ##STR3## the addition salts and stereochemically isomeric forms thereof, said compounds having antipicornaviral activity.