Compounds of formulae (1a) and (1b) are described: in which the dashed line represents an optional bond; A is a --N.dbd. atom or a --N(R.sup.b)--, --C(R.sup.b).dbd. or --C(R.sup.b)(R.sup.C)-- group; R.sup.a, R.sup.b and R.sup.c is each independently a hydrogen atom or an optionally substituted C.sup.1-6alkyl group; X is an --O-- or --S-- atom or --NH-- group or substituted N atom; each Y is independently a N atom or CH group or substituted C atom; n is zero or the integer 1; Alk.sup.1 is an optionally substituted aliphatic or heteroaliphatic chain L.sup.1 is a covalent bond or a linker atom or group; Cy.sup.1 is a hydrogen atom or an optionally substituted cycloaliphatic, polycycloaliphatic, heterocycloaliphatic, polyheterocycloaliphatic, aromatic or heteroaromatic group; Ar is an optionally substituted aromatic or heteroaromatic group; and the salts, solvates, hydrates and N-oxides thereof; The compounds are potent inhibitors of p38 kinase and are use in the prophylaxis or treatment of p38 kinase mediated diseases or disorders, such as rheumatoid arthritis ##STR00001##