The systemic mycoses like paracoccidioidomycosis and histoplasmosis, are the main cause of adrenal insufficiency in the countries where they arc endemic. In Venezuela an elevated frequency of these mycoses has been registered. The objective of this study was to evaluate the glucocorticoid adrenal function in patients with paracoccidioidomycosis and histoplasmosis hospitalized in the University Hospital "Ruiz y Pácz" of Ciudad Bolivar (Bolivar state) and in the Hospital "Luis Felipe Rojas Guevara", of El Tigre (Anzoátegui state), Venezuela, between January 2003 and January 2004. The test of fast stimulation with synthetic adrenocorticotrophin hormone (ACTH) was applied to a total of 12 patients with diagnosis of some of these mycoses and data of epidemiologic interest were taken. The proportion men:women was of 5:1, the average age was 35.1 +/- 0.37 years, similar to the control group. Basal plasmatic cortisol levels were within the normal rank in all the patients. After the injection of synthetic ACTH, an increase of plasmatic cortisol values in the same rank for patients with a normal adrenal function was observed, but it was significantly lower than the observed for the control group. These results suggest that there is an adrenal gland functional reserve diminution in patients with either Paracoccidioidomycosis or Histoplasmosis. In patients with systemic mycoses, it is important to evaluate the response to the test of fast stimulation with ACTH due to the frequency of impairment of the glucocorticoid adrenal function in our location.