Compounds of formula (I): ##STR00001## wherein: Q represents an optionally substituted 5- or 6-membered aryl or heteroaryl ring; X represents O, S, NR.sup.5 or CR.sup.6 R.sup.7; Y represents CHOH, CHSH, NOR.sup.8, CNR.sup.8 or CNOR.sup.8; Z represents a bond, CR.sup.10R.sup.11, O, S, SO, SO.sub.2, NR.sup.10, OCR.sup.10R.sup.11, CR.sup.10R.sup.11 O or Z, R.sup.4 and Q together form an optionally substituted fused tricyclic group; R.sup.1, R.sup.1', R.sup.3 and R.sup.3' each independently represents H, C.sub.1-6 alkyl or C.sub.1-4 alkylaryl; R.sup.2 represents CO.sub.2R.sup.8, CONR.sup.5OR.sup.9 or NR.sup.5COR.sup.9; R.sup.4 represents optionally substituted 5- or 6-membered aryl or heteroaryl; R.sup.5 represents H or C.sub.1-3 alkyl; R.sup.6 and R.sup.7 each independently represents H, C.sub.1-3 alkyl or halo; R.sup.8 represents H or C.sub.1-2 alkyl; R.sup.9 represents H or C.sub.1-3 alkyl; R.sup.10 and R.sup.11 each independently represents H, C.sub.1-6 alkyl or C.sub.1-4 alkylaryl; and physiologically functional derivatives thereof, processes for their preparation, pharmaceutical formulations containing them and their use as inhibitors of matrix metalloproteinase enzymes (MMPs) are described.