Enzymoimmunoassays have been developed as alternatives to radioimmunoassays because they obviate the need for labelled compounds yet offering comparable specificity. The authors used an enzymoimmunoassay to investigate hourly serum cortisol levels over 24 hours in 6 patients (aged over 40 years) with endogenous depression (4 unipolar depressions, under antidepressor treatment and 2 bipolar depressions, without medication) and in 2 controls, aged 20 and 47 years. In agreement with literature data, a clear circadian rhythm was observed in controls and in the depressed patients, and hypercorticism was noted in one depressed patient. A trend towards phase advance in depression was seen in both the treated and untreated patients.