A hydrate of 5-[4-[2-(N-methyl-N-(2-pyridyl)amino)ethoxy]benzyl]thiazolidine-2,4-dione- , maleic acid salt., characterized in that it: (i) comprises water in the range of from 0.3 to 0.6 molar equivalents; and (ii) provides an infra red spectrum containing peaks at 1757, 1331, 1290, 1211 and 767 cm.sup.-1; and/or (iii) provides a Raman spectrum containing peaks at 1758, 1610, 1394, 1316 and 1289 cm.sup.-1; and/or (iv) provides a solid state nuclear magnetic resonance spectrum containing chemical shifts substantially as set out in Table I herein; and/or (v) provides an X-ray powder diffraction (XRPD) pattern substantially as set out in FIG. IV herein; 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.