There is provided a novel series of synthetic antagonistic analogs of
hGH-RH(1-29)NH.sub.2. These analogs inhibit the activity of endogenous
hGH-RH on the pituitary GH-RH receptors, and therefore prevent the
release of growth hormone. The analogs also inhibit the proliferation of
human cancers through a direct effect on the cancer cells. The higher
inhibitory potencies of the new analogs, as compared to previously
described ones, results from replacement of various amino acids.