We compared the spontaneous behaviour (motility, adhesiveness, locomotion) and the chemotactic responses of exudate and blood-borne neutrophils. Directional locomotion of exudate neutrophils in 2% HSA-Gey's towards exudate fluid was not significantly changed, the response to activated autologous plasma diminished, and that to f-Met-Leu-Phe (10(-9) M) increased in comparison with blood-borne cells. The spontaneous behaviour of exudate cells in 2% HSA-Gey's (no gradient) differed markedly from that of blood-borne cells. In tissue culture medium (2% HSA-Gey's) exudate cells showed heightened motility in suspension and greater adhesiveness to glass substrata. These differences were eliminated by culturing the cells in their physiological media (i.e. plasma or exudate fluid). In contrast to blood-borne cells, exudate neutrophils tended to aggregate spontaneously. There was no correlation between neutrophil aggregation and adhesion to glass substrata of exudate cells in exudate fluid.