Certain metabolic abnormalities are common to all malignant cells, and Horrobin proposed that the underlying cause is the inability of cancer cells to produce prostaglandin E1 (PGE1). This appears to be due to the lack of the enzyme delta-6-desaturase which converts the essential fatty acid, linoleic acid, to gamma-linolenic acid (GLA), from which PGE1 is then synthesized. Our studies strongly support this contention. Addition to GLA to cancer cells, thus bypassing the block in the metabolic pathway, results in very marked, statistically highly significant inhibition of growth, while having no effect at all on normal cells. Our finding of the regression of cancer through such proposed normalization offers preliminary hope for a new effective and harmless approach to the treatment of cancer.