Fabry's disease is characterized by an inherited X-linked disorder of glycosphingolipid catabolism, and heterozygous women affected with this disease who show overt symptoms including cardiac manifestations have rarely been reported. To elucidate the features of myocardial involvement in female patients, noninvasive techniques including exercise stress thallium-201 myocardial scintigraphy were performed. Three female patients, Cases 1-3, 26, 29 and 50 years of age, were documented low leucocytic alpha-galactosidase activities of less than 48% of normal (67.92-16.2 nmol/mg protein/h). They were examined using ECG, two-dimensional echocardiography (2-D Echo), Holter ECG, treadmill test and stress scintigraphy. On the ECG, negative T waves were shown in leads III and aVF in Cases 1 and 2. Left ventricular high voltage, giant negative T waves and short PR intervals were seen in Case 3. The 2-D Echo revealed neither valvular change nor left ventricular hypertrophy. On the Holter ECG, monofocal ventricular premature beats were occasionally observed in Cases 1 and 3. The treadmill test showed positive ST changes only in Case 2. On the exercise stress scintigraphy, uptake of thallium-201 was enhanced in the apex of the heart in Cases 2 and 3. Low uptake areas of thallium-201 were observed in Case 3. The ventricular angiogram revealed slight hypertrophy of the wall of the apical portion. In endocardial biopsies from the right ventricle, myelinoid lamellar inclusions were demonstrated in myocardial cells electron microscopically. Increased uptake of thallium-201 in the apex was noted in two of the three patients, but no apical thickening was noticed in any of the three cases by 2-D Echo. From the result of the biopsy of Case 3, the increased apical uptake of thallium-201 seems to reflect thickening caused by the deposition of glycosphingolipid. It was concluded that myocardial involvement in female Fabry's disease may occur early in the third decade and that the lesions could be detected with high sensitivity by thallium-201 myocardial scintigraphy.