Vasoactive intestinal polypeptide (VIP) was measured in extracts from polymorphonuclear (PMN) and mononuclear (MN) leucocytes from 14 healthy persons and 12 pigs. In addition, extracts from PMN and MN cells from eight pigs were studied for possible contents of somatostatin. Immunoreactive VIP was present in the PMN and MN leucocytes from man and pigs with a significantly higher level in the MN cells. Similarly, immunoreactive somatostatin was found in both cell lines from pigs with a significant higher amount in the MN leucocytes. Furthermore, extracts from pure populations of human PMN and MN leucocytes were separately applied on a Sephadex G-50 Fine column, and VIP, somatostatin, secretin, GIP and motilin were measured in the eluted fractions. Only VIP and somatostatin were found to be present in detectable amounts. Immunoreactive VIP eluted corresponding to the elution volume for pure porcine VIP in extracts from both PMN and MN cells, while immunoreactive somatostatin eluted corresponding to the elution volume for the synthetic tetradecapeptide somatostatin in extracts from MN cells only. Possible physiological implications of these findings are briefly discussed.