The motile behavior of 24 human leukemia cell populations was recorded by means of time-lapse cinematography. Three basic modes of motility were considered in the evaluation: surface motility, on spot motility and, the translocative form, locomotion. While surface motility was displayed by all cells in good condition, the number of cells engaged in on spot motility and in locomotion was different for each leukemia and comprised a range from zero to near complete. In addition to this numerical aspect, the existence of cell-dependent modes of locomotion became evident. Based on a characteristic configuration, blast cells, promyelocytes, myelocytes, and granulocytes together with small, non-stimulated lymphocytes had their distinct locomotive patterns. On the other hand, blast cells of different origin were indistinguishable in their manner of movement. Thus, each leukemia presented its individual pattern of motility that was determined not only by the presence of one or more cell classes with specific modes of locomotion, but also by their numbers involved in this activity. This individuality was found to occur irrespective of the hematological diagnosis and could not be predicted. Whether there is any interrelation between the differing patterns of motility and the clinical course of a given leukemia remains to be established.