In 3 patients with brain tumors involving language areas, we investigated functional cortical regions and epileptogenic foci using subdural electrode stimulation before operation. These stimulation studies were useful in preserving postoperatively their language function. The following neuropsychological findings were obtained; (1) Stimulation of Broca area (Brodmann 44 and 45) did not produce anarthria (phonetic disintegration), but semantic and phonemic parahasias and word finding difficulties. (2) Stimulation of lower motor cortex elicited anarthria. (3) Buccofacial apraxia was not produced only by stimulation of frontal operculum. (4) When anarthria was elicited by stimulation, difficulty in retrieving both Kana and Kanji letter-forms and paragraphia in Kana letters were sometimes observed. (5) Stimulation at Exner's writing centre did not produce writing deficits, but elicited word finding difficulties and paraphasias.