A new sorting task designed to isolate and measure specific components of problem-solving ability was administered to four subject groups: patients with focal frontal lobe lesions, patients with both frontal dysfunction and amnesia (Korsakoff's syndrome), patients with circumscribed (non-Korsakoff) amnesia, and normal control subjects. The patients with circumscribed (non-Korsakoff) amnesia, and normal control subjects. The patients with frontal lobe lesions and patients with Korsakoff's syndrome were impaired on eight of the nine components of the task. The findings run counter to theories of a single or primary impairment in patients with frontal lobe dysfunction. Rather, the results suggest that a wide spectrum of deficits in abstract thinking, cognitive flexibility, and use of knowledge to regulate behavior contributes to the problem-solving impairment of these patients. Although the (non-Korsakoff) amnesic patients performed similarly to normal subjects on most measures, a finer analysis suggested that successful performance on this complex sorting task, in addition to being strongly dependent upon frontal lobe function, is mildly dependent upon memory function.