A new method to investigate periods and their variations is proposed. The phase curve is approximated by the cubic
spline-functíon with fixed number of equidistantly distributed in phasev characteristic points. Because such a smoothing function depends on the value of the Inltial epoch it is proposed to use the mean of some spline-curves corresponding to various initial epochs for the approximation. The mean guadratic deviation of observatlons from this best fit curve serves as the test function. The best fit phase deviations of the 'season sets’ of observations are used to study period variations.