The patterns of cell activity recorded extracellularly in the motor cortex of behaving monkeys were classified into the following three groups using a combination of cluster and discriminant analyses of 1925 spike trains: (a) cells with low discharge rate and low bursting (67.1%), (b) cells with low discharge rate but bursting (20.2%), and (c) cells with high discharge rate and low bursting (12.7%). The percentage of directionally tuned cells and of cells engaged during a memorized delay task were very similar in all three cell groups.