The invention provides methods of investigating a mechanism of action of a compound, which includes providing a device for monitoring cell-substrate impedance; attaching the device to an impedance analyzer; adding cells to two or more wells; adding a test compound to at least one of the wells and providing at least one control well; monitoring impedance of the wells to obtain a series of impedance measurements; plotting impedance measurements to obtain impedance curves and comparing the impedance curves to determine a time frame at which the test compound has a significant effect on cell growth or behavior. Determining the time frame provides information on changes in cell status in response to the test compound, including cell attachment or adhesion status, cell growth or proliferation status, the number of viable or dead cells, cytoskeletal organization or structure, and the number of cells going through apoptosis or necrosis.