To study the role of medial frontal cortex in learning and memory of sequential procedures, we examined neuronal activity of the presupplementary motor area (pre-SMA) and supplementary motor area (SMA) while monkeys (n = 2) performed a sequential button press task, "2 x 5 task." In this paradigm, 2 of 16 (4 x 4 matrix) light-emitting diode buttons (called "set") were illuminated simultaneously and the monkey had to press them in a predetermined order. A total of five sets (called "hyperset") was presented in a fixed order for completion of a trial. We examined the neuronal activity of each cell using two kinds of hypersets: new hypersets that the monkey experienced for the first time for which he had to find the correct orders of button presses by trial-and-error and learned hypersets that the monkey had learned with extensive practice (n = 16 and 10 for each monkey). To investigate whether cells in medial frontal cortex are involved in the acquisition of new sequences or execution of well-learned procedures, we examined three to five new hypersets and three to five learned hypersets for each cell. Among 345 task-related cells, we found 78 cells that were more active during performance of new hypersets than learned hypersets (new-preferring cells) and 18 cells that were more active for learned hypersets (learned-preferring cells). Among new-preferring cells, 33 cells showed a learning-dependent decrease of cell activity: their activity was highest at the beginning of learning and decreased as the animal acquired the correct response for each set with increasing reliability. In contrast, 11 learned-preferring cells showed a learning-dependent increase of neuronal activity. We found a difference in the anatomic distribution of new-preferring cells. The proportion of new-preferring cells was greater in the rostral part of the medial frontal cortex, corresponding to the pre-SMA, than the posterior part, the SMA. There was some trend that learned-preferring cells were more abundant in the SMA. These results suggest that the pre-SMA, rather than SMA, is more involved in the acquisition of new sequential procedures.