In a study of healthy human individuals a complete lack of correlation between the results of the agarose leukocyte migration inhibition (LMI) test, using purified protein derivative (of tuberculin) (PPD) and Bacillus Calmette Guérin (BCG) as antigens, and delayed cutaneous hypersensitivity and lymphocyte transformation in vitro to PPD was found. There was a reasonable correlation between PPD- and BCG-induced LMI. Antibodies to PPD proved to have no influence on PPD-induced LMI. Purified polymorphonuclear leukocytes, whether derived from donors sensitive to PPD in the agarose LMI test or from nonsensitive donors, did not show migration inhibition to PPD. It was concluded that polymorphonuclear leukocytes and lymphocytes need to be present simultaneously for migration inhibition of peripheral blood leukocytes by PPD. Furthermore, because a consistent relation with conventional parameters of cell-mediated immunity was lacking, it is doubtful whether the agarose LMI test can be considered as an alternative parameter of this kind of immunity.