Twenty-eight severely ill, hospitalized Nigerian patients, 18 males and 10 females with a median age of 41 years (group I) and 20 stable ambulatory patients, 11 males and 9 females with a median age of 42.5 years (group II), had early morning plasma cortisol measurements. Ten healthy young Nigerian males with a mean age of 22.1 years (group III) had plasma cortisol estimations during insulin tolerance test. The mean (+/- SD) cortisol values for the three groups in nmols/l were as follows: group I--389.3 (202.4), group II--267.1 (67.4), group III-624.5 (81.1). The results for the group III healthy controls represent the peak (60 mins) value during insulin induced hypoglycemic stress. A one way analysis of variance (ANOVA) demonstrated a statistically significant difference between the three mean cortisol values, P < 0.001. A pair-wise comparison using the t-test also showed significant differences between the groups, P < 0.05 in each case. An important observation was the variable pattern of cortisol stress response in different types of illnesses. Cases of stroke appeared to be associated with increased cortisol stress values (Z-score + 5.67) while patients with hypotension (B.P. < or = 90/60) and those on Rifampicin had reduced cortisol responses (Z-scores - 3.66 and 3.51 respectively). However, no firm recommendations can as yet be made regarding the usefulness of corticosteroids in life-threatening illnesses among Nigerians, other than those for which steroids are known to beneficial.