AbstractThe procedure for the precipitation of molecules supported on MeOPEG (molecular mass 5000) and their purification by fractional crystallization has been made easier by use of microwave irradiation. A correct choice of the solvent employed for reaction or purification (DME, THF, 1,2‐dichlorobenzene, iPrOH, ethylene glycol) allows working with 10 g of MeOPEG‐OH, dissolved in 100 mL of solvent, under microwave irradiation conditions and for crystallization to be induced just by removal of the reaction flask from the microwave oven. No additional precipitation solvents are needed, thus reducing the reaction times and the potential hazards of working with large amounts of flammable solvents. The syntheses of several peptides and of a tetrasubstituted pyridine are reported. Large amounts of MeOPEG‐OH may be used in this procedure, and so polyethylene glycol assisted organic synthesis can be regarded as a valid preparative technique. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)