There are many ways of analyzing flow cytometry data. The first and probably most important packages are those provided on the instruments used in the laboratory to collect the initial data. Often the manufacturer provides a limited analysis package, however, frequently a great deal of the needed analysis can be obtained directly from the instrument package. If more complex gating and comparison are required, it is mostly necessary to move the data to an off-line computer with an alternative data analysis package. Many freeware packages are available today that are excellent. Several examples are WinMDI written by Joe Trotter.