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Leucocyte activation by different agents does not result in a uniform pattern of parallel responses. Some activities have synergistic and others antagonistic effects on directional locomotion in vitro. No reliable correlation between chemotaxis on the one hand and other leucocyte activities such as crawling movements, adhesion to solid substrata and chemokinesis has been firmly established. Therefore, the assessment of chemotaxis by measuring orientation is presumably the only reliable quantitative measure for chemotaxis.

Neutrophils from patients with acute bacterial infections show a marked decrease in random as well as directional locomotion in vitro. The further analysis of the data suggests that defective directional locomotion is due to impaired locomotion and not to impaired chemotaxis. The defect disappeared almost completely with clinical recovery. There was no direct correlation between impaired directional neutrophil locomotion and the proportion of band forms in the neutrophil population. Plasma obtained from patients with acute bacterial infections showed no 'spontaneous' chemotactic activity and immune complex-induced cytotaxin formation was normal in vitro. Neutrophils from 2 patients with viral pneumonia showed normal locomotion.

The effect of chemotactic peptides which lack chemokinetic activity has been investigated. The neutrophil response is proportional to the logarithm of the stimulus intensity, or alternatively a power function with an exponent of 0.3. Equal responses are obtained for equal ratios between the peptide concentration in the lower compartment and the threshold concentration. The significance of Weber-Fechner's law in leucocyte chemotaxis is discussed.

Evidence has been presented to show that chemokinesis and chemotaxis of human neutrophil granulocytes can be controlled by distinct cellular mechanisms and by different chemicals. Materials such as human serum albumin or fibrinogen had chemokinetic but no chemotactic properties. Highly purified preparations of serum-derived peptides containing classical anaphylatoxin had detectable chemotactic activity only. Chemokinetic as well as chemotactic substances were required for the expression of chemotaxis in the form of efficient directional locomotion. The roles of chemokinesis and chemotaxis in the regulation of directional locomotion have been analyzed. Further experiments showed that the chemotactic response conforms to the law of Weber-Fechner. The number of cells which had accumulated in response to a chemotactic simulus was proportional to the logarithm of the concentration of the chemical substance. Readaptation from high to low chemotactic stimulus occurred only to a limited extent.

Neutrophils separated from Hageman factor-deficient blood exhibit normal random and directional locomotion. No defect in cytotaxin formation could be demonstrated in Hageman factor-deficient plasma, nor did kallikrein inhibitor interfere with the chemotactic activity of normal immune complex-activated human plasma. The results suggest that the chemotactic activity which is detectable in unfractionated human plasma is not derived from Hageman factor-dependent pathways.

Experiments performed by means of time lapse cinematography or the filter technique show that human serum albumin has marked chemokinetic effects on neutrophil cultured in Gey's solution. The average speed of the cells, as well as the proportion of neutrophils showing locomotion, is increased. Enhanced locomotion correlates with decreased attachment to the substratum as determined by morphological and functional criteria.