In the present work we have evaluated the effect of decreasing concentrations of normal plasma in TC 199 on leukocyte capillary migration. From the 1st to the 4th hour of migration, normal plasma at 100%-80%-60%-40% concentration, significantly inhibits leukocyte migration. The inhibitory effect is lost, only by a few plasmas, at 60% and 40% concentration, during the following migration hours. Normal plasma at 20% and 10% concentration doesn't show any inhibitory effect on leukocyte capillary migration. Therefore, for clinical studies on pathological plasmas we recommend the use o plasma at 20% or 10% concentration to avoid aspecific inhibition.