The effect of continuous (50 micrograms and 100 micrograms/4 hrs) versus pulsatile (6.25 micrograms every 30 minutes equivalent to a total dose of 50 micrograms during 4 hours) administration of ovine corticotropin releasing factor (oCRF) was investigated in 6 healthy, male subjects. A rise in the plasma concentrations of ACTH and of cortisol was observed during the intermittent, but not during the continuous infusion of 50 micrograms oCRF/4 hours. Comparing the rise in the plasma concentrations of ACTH and cortisol above individual basal concentrations no differences were found between the continuous infusion of 100 micrograms oCRF and the pulsatile administration of 50 micrograms oCRF. Response to pulsatile (50 micrograms/4 hrs) and continuous (100 micrograms/4 hrs) administration of oCRF, but lack of response to continuous infusion at a rate of 50 micrograms/4 hrs was also reflected by the calculated mean sum of increments of cortisol above individual basal concentrations. These results indicate a superior efficacy of intermittent versus continuous administration of oCRF in healthy man.