Ornithine decarboxylase and histidine decarboxylase, the enzymes involved in the formation of putrescine and histamine from their respective precursor amino acids are widely distributed in the female reproductive tract and are frequently associated with rapidly growing tissues. The relationship between the two amines and their associated metabolic enzymes is not clearly understood but there is often an apparent reciprocal relationship between the distribution of the two decarboxylases suggesting that histamine and putrescine may, in some circumstances, be serving broadly similar functions in their respective target tissues. The comparative distribution and hormonal regulation of ornithine and histidine decarboxylases in the reproductive tract during pregnancy and in other rapidly growing tissue will be investigated with particular emphasis on the embryo and placenta. A number of cell lines will also be investigated so that the mechanisms of hormonal regulation may be studied under conditions where the environment is more amenable to precise manipulation than is possible in vivo. The similarities between steroid and polypeptide stimulation of ornithine and histidine decarboxylases will be clarified and the relative importance of translation vs transcription in the hormonal control of these enzymes will be established.