In order to test the possible effects of an intravenous administration of substance P (SP) on basal and TRH-stimulated PRL release, SP was infused alone (0.5 or 1.5 pmol/kg<sup>-1</sup>/min<sup>-1</sup> for 60 min) or after TRH (20 or 400 µg in an i.v. bolus) in 21 normal male subjects. In addition, plasma cortisol levels during SP infusion were measured. In agreement with previous findings, a significant increase in plasma cortisol levels was observed when the higher (1.5pmol/ kg<sup>-1</sup>/min<sup>-1</sup>) but not the lower (0.5 pmol/kg<sup>-1</sup>/min<sup>-1</sup>) amount of SP was given. In contrast, basal and TRH (20 or 400 µg)-induced PRL release were not modified by SP at any tested amount. These data suggest that, in normal men, plasma SP is not involved in the control of PRL release at the anterior pituitary level.