A study was initiated to explore possible differences in handling telomere attrition in the most commonmalignant and benign tumours of the breast in Malaysian women. Infiltrating ductal carcinoma (IDC) andfibroadenoma (FA) represented the malignant and benign prototypes respectively. 29 IDC, 28 FA and 22 benignnon-lesional control (BNL) breast tissue samples were analysed for telomerase activation using a Telomerase PCRELISA kit (Boehringer Mannheim). In addition, 23 IDC, 12 FA and 14 BNL were subjected to telomere lengthdetermination with a TeloTAGGG Telomere Length Assay Kit (Roche Diagnostic GmbH, Germany), followingdigestion of genomic DNA by frequently cutting restriction enzymes RsaI and HinfI. Mean telomerase activityin IDC (A450nm=0.3338), but not FA (A450nm=0.0003) was significantly raised (p<0.05) compared with BNL(A450nm=0.0031). Similarly IDC (1.2 kb), but not FA (2.2 kb), showed significant telomere shortening (p<0.05)relative to BNL (2.9 kb). The findings imply that telomere attrition and telomerase activation differ betweenmalignant and benign tumours of the breast and may be important for targeted therapy.