Methylcyclopentadienyl Manganese Tricarbonyl (MMT) is currently in use as an octane 'trimming' agent. The Environmental Monitoring and Support Laboratory (EMSL) of EPA is currently monitoring manganese (Mn) levels of gasolines sampled from service stations throughout the United States. The results of this survey have shown that an increasing percentage of the samples taken contain sufficient Mn to indicate MMT has been used to 'trim' the octane of that sample. The latest sampling report (September, 1976) indicated 10% of the samples taken during the first half of 1976 contained significant Mn levels. This coupled with predictions of much greater use by the oil companies necessitated EPA requiring MMT be present in Certification service accumulation fuel beginning with the 1979 model year. EPA has been very interested in the MMT developments, especially because of the results of a number of EPA and industry studies that have recently been completed or are currently in progress. Some of the results from these studies show a potential negative influence of MMT on exhaust emissions. In order to more fully evaluate the research results of these industry studies, the Emission Control Technology Division of the EPA Office of Mobile Source Air Pollution Control invited the submission of MMT/emission control related data that has been developed by various companies.