The invention provides stable formulations of pemetrexed for infusion. The formulations are based on using pemetrexed diacid and certain selected suitable stabilising basic amine compounds that provide counter ions to the pemetrexed diacid, forming base addition salts. The formulations can be dried powder formulations to be reconstituted as liquid concentrate formulations or directly in ready-to-use infusion solutions, or they can be liquid formulations, most suitably concentrates to be diluted in infusion solution prior to use. The suitable basic amine addition compounds according to the invention are one or more of diethanolamine, tris-(hydroxymethyl)aminomethane and meglumine.
