1982). In contrast, healthy humans do not show a TRH-induced increase in circulating cortisol concentration, whereas in some people with PDH administration of TRH does result in an increased plasma cortisol concentration (Krieger and Luria 1977; Pieters et al. 1979). Originally, it was hypothesized that humans with TRH-induced secretion of cortisol would have a PI tumor, comparable to PPID in horses. However, a later study did not demonstrate that Cushing patients with TRH-induced cortisol secretion were more likely to have a PI tumor (Pieters et al. 1982). The gene discussed is TRH; the disease is neoplasm.