Migration is a prerequisite for blood monocytes to exert their biological activities, since they have to migrate from blood into the tissues where they transform into macrophages. In vivo chemotaxis of blood monocytes is seldom evaluated, while their in vitro ability to migrate is frequently tested. The most frequently used test relies on BM migration through filters using modified Boyden chemotactic chambers. Using checkerboard analysis it is possible to define chemotactic and chemokinetic factors.