Studies over many years have suggested that increased polyamine synthesis may be necessary for neoplastic growth. This review summarizes recent work on the regulation of putrescine production both de novo and via the degradation of higher polyamines and provides a summary of studies using transgenic mice in which the levels of proteins that regulate these processes (L-ornithine decarboxylase, antizyme and spermidine/spermine-N(1)-acetyltransferase) are altered.