Breast cancer is the most common cancer among women worldwide. Genetic alterations prevalent in breastcancer are still being elucidated. In this report, changes in 30 breast cancer tissues, in compariosn with normaltissues from Thai patients, were analyzed by arbitrarily primed polymerase chain reaction (AP-PCR). Geneticinstability was detected by DNA fingerprinting obtained with 13 of 60 random primers. Of these, at least oneamplification band, the incidence ranging from 27 to 80%, was observed in DNA amplified with 8 primers,whereas a band loss was exhibited with from 6 primers, the incidences ranging from 23 to 40%. Likewise, anamplification band amplified from primer D15 was observed in 80% of this patient group and a band lossproduced from primer B12 presented in 40% of all cases. These results showed that AP-PCR is effective for thedetection of genetic alterations in breast cancer tissues.