The blood-brain-barrier has been the major obstacle to successfully deliver active chemotherapeutic agents. Moreover, the limited benefit derived from chemotherapy is associated with severe side effects. TMZ is an orally administered alkylating agent that plays an important role in the standard therapy of malignant gliomas. It has a good blood-brain-barrier penetration which results in OTX015 therapeu-tic concentrations within the central nervous system and confers manageable side effects. The possible role of TMZ in the treatment of brain metastases is currently being explored. Several studies on utilizing TMZ in patients with brain metastases describe rather variable outcomes. Although MGMT promoter methylation is known to be a predictive factor for the success of using alkylating substances like TMZ in malignant gliomas, MGMT promoter methylation of brain metastases has not been explored in depth. Most studies on MGMT promoter methylation rely on the methylation-specific polymerase chain reaction assay. Other investigators prefer the somewhat simpler approach to detect the function of the MGMT gene by means of immunhistochemistry. However, data addressing both, MGMT promoter methylation and MGMT immunoreactivity,Cycloheximide are sparse and controversially discussed. Consequently, we aimed here to investigate comprehensively MGMT promoter methylation and MGMT immunohistochemistry in brain metas-tases derived from lung, breast and renal cell carcinomas as well as from malignant melanomas. Detection of the MGMT methylation status by 80 cycles of a nested PCR, as recommended for DNA isolated from formalin-fixed paraffin-embedded tissue, may easily increase the frequency of sampling error, thus negatively influencing the reliability of results obtained by MS-PCR. This may explain as to why only 61.2% of our samples were evaluable by MS-PCR and why only in 75% of the cases replicate experiments on 20 randomly selected tumor samples yielded reproducible results. Despite such limitations MS-PCR on FFPE has been shown to be a valid and trustable technique resulting in reproducible data, which closely mirrors results obtained by MS-PCR on fresh frozen tissue.