Abstract: Novel pro-drugs to new and unnatural dipeptoids of .alpha.-substituted Trp-Phe derivatives useful as agents in the treatment of obesity, hypersecretion of gastric acid in the gut, gastrin-dependent tumors, or as antipsychotics are disclosed. Further, the dipeptoids are antianxiety agents and antiulcer agents. They are agents useful for preventing the response to the withdrawal from chronic treatment or with use of nicotine, diazepam, alcohol, cocaine, caffeine, or opioids. The pro-drugs are also useful in treating and/or preventing panic attacks. Also disclosed are pharmaceutical compositions and methods of treatment using the pro-drugs as well as processes for preparing them and novel intermediates useful in their preparation. An additional feature of the invention is the use of the subject pro-drug compounds in diagnostic compositions.