Both growth hormone (GH) and prolactin (PRL) modulate immune responses in vitro. We studied chemotaxis under agarose of polymorphonuclear cells from patients with acromegaly or hyperprolactinemia. Polymorphonuclear cells were purified by dextran sedimentation and subjected to stimulation with N-formylmethionyl-phenylalanine. The results showed a decrease in both directed migration (acromegaly: 971 +/- 155 microns; hyperprolactinemia: 1123 +/- 137 microns, expressed as mean +/- SEM) and spontaneous migration (acromegaly: 270 +/- 77 microns; hyperprolactinemia: 298 +/- 77 microns) when compared to similar features from normal controls (directed migration: 2019 +/- 99 microns; spontaneous migration: 590 +/- 49 microns) and from patients with non-GH/PRL-secreting pituitary tumours (directed migration: 1633 +/- 282 microns; spontaneous migration: 562 +/- 116 microns), suggesting that this defect is selective for acromegaly and hyperprolactinemia. Our results point to a putative direct or indirect effect of GH and PRL on polymorphonuclear cell chemotaxis.