The study was carried out under direct videomicroscopic control to ascertain whether electromagnetic forces (photons) can initiate directed cell motility of human polymorphonuclear neutrophils (PMN). Cell suspensions containing a mixture of randomly motile white blood cells and erythrocytes (red cells) were placed in a double-decked preparation created by a glass slide and two cover slips and sealed by paraffin. Erythrocytes in the upper or lower chamber were destroyed by a single burst from a narrow ruby laser beam. Directed locomotion of PMN toward the erythrocyte debris occurred exclusively in the chamber in which the erythrocytes had been destroyed. Only random PMN locomotion was observed in the adjacent chamber. The results indicate that in this experimental model, electromagnetic forces do not initiate directed locomotion.