Methionine adenosyltransferase (MAT III), also known as S-adeno-sylmethionine synthetase, was purified from rat liver and crystallized. X-ray diffraction data were collected using a microfocused synchrotron radiation. The crystallization conditions were extensively optimized but final crystal size was never larger than 303 pm3. Due to their small size crystals had no detectable diffraction on either rotating anode source or the Deresbury SRS beamline 9.6 (GB). Finally, four data sets were collected on Grenoble ESRF (France) undulator microfocus beamline ID13 to resolution of 3.2-3.6 Å. Crystals belong to the cubic space group F432 with cell dimension a = 246 Å. Attempts are under way to solve the structure by molecular replacement, using recombinant MAT I rat liver structure as a search model