The preparation of some water soluble analogues of the tumour growth inhibitory hexamethylmelamine is described. The ultra-violet absorption characteristics, solubility and n-octanol/water partition coefficients of these new derivatives and some related compounds have been determined. Rates of demethylation by a liver microsomal preparation and anti-tumour assays against the ADJ/PC6A mouse plasma cell tumour and a human lung tumour xenograft are reported. Two of the derivatives, pentamethylmelamine and N2, N4, N6-trimethyl-N2, N4, N6-trimethylolmelamine, which have shown activity against the xenograft are potential candidates for clinical trials using the intravenous route of administration.