A hydrate of 5-[4-[2-(N-methyl-N-(2-pyridyl)amino)ethoxy]benzyl]thiazolidine-2,4-dione- , maleic acid salt, characterised in that it: (i) comprises water in the range of from 0.4 to 2.5% w/w; and (ii) provides an infra red spectrum containing peaks at 1749, 1703, 1645, 1623, 1365 and 736 cm.sup.-1; and/or (iii) provides an X-ray powder diffraction (XRPD) pattern substantially as set out in FIG. II and/or (iv) provides a Raman spectrum containing peaks at 3106, 3069, 3002, 2961, 1750, 1718, 1684, 1385, 1335, 1229, 1078, 917, 428 and 349 cm.sup.-1 and/or (iv) provides a solid-state nuclear magnetic resonance spectrum containing chemical shifts substantially as set out in Table I; a process for the preparation of such a compound, a pharmaceutical composition containing such a compound and the use of such a compound or composition in medicine.