Many stars continuously eject material and thus surround themselves with a stellar wind. We can observe this wind indirectly through its characteristic effects on the stellar spectrum. In particular, this mass flow influences the line profiles. These so called P-Cygni profiles can be observed in the visual part of the spectrum of early-type stars and Wolf-Rayet stars, as well as - and even more clearly - in the ultraviolet part. In order to study the stellar wind structure, a computer programme was written which calculates theoretical P-Cygni profiles using the Comoving Frame Method. As input, this code can use the results obtained from other programmes, such as a non-LTE code. Through parameter adjustments a fit to an observed profile can be made.