Various methods are discussed for the problem of obtaining the parameters of relaxing systems which exhibit two lifetimes with different weights using modulation methods. A graphical method is described which enables all four parameters to be obtained from the plots of inverse signal against the square of the modulation frequency. It is shown that a least squares curve fitting method to the experimental data is in general the best of the methods outlined. Some data are presented for the relaxation parameters of a riboflavin and semiquinone mixture.