The enteropooling activity of soya-peptone was studied in germfree piglets. The enteropooling activity was restricted to the proximal part of the jejunum and was found to be blocked by aspirin. The hypothesis that soya-peptone acts via an increased biosynthesis/release of prostanoids was further studied using guinea-pig lung parenchyma. In this tissue soya-peptone induces the release of TXB2, which was inhibited by indomethacin (3 microM). The involvement of cholinergic, histaminergic and serotonergic pathways in the soya-peptone-mediated response was excluded, using antagonists. The conclusion was reached that soya-peptone can stimulate/modulate the biosynthesis of cyclic eicosanoids and that it exerts its enteropooling activity via the same mechanism in the jejunum of piglets.