New Michigan legislation permits an officer to make a warrantless arrest for a misdemeanor assault at the scene of certain domestic disturbances even if the officer did not witness its commission. 'Reasonable cause' is instead required for the officer to believe that certain specified fact patterns had occurred. To ensure that police have access to information about repeat domestic violence offenders, all judicial notices of divorce-related injunctions and peace bonds are to be filed with local police departments. All of the operative provisions of the statute provide responding officers with discretion in their handling of a domestic crisis. By most standards, the Detroit Police Department adopted the formal requirements of the new legislation through the implementation of appropriate regulations and training. Preliminary data in an analysis of monthly reports of runs, arrests, and fatalities suggest that the legislation has not resulted in an increase in domestic violence runs or arrests. In fact, there has been a decline. Followup research is required to determine if this is due to increased call screening, better dispute resolution short of arrest, or a statistical artifact. Training was found to markedly affect the attitudes of officers toward intervention in a domestic violence incident. The department should develop an evaluation system that puts a systematic weight to the officer's handling of familial violence and similar social service functions. Tabular data and 29 references are provided.