In Germany we observe a decline in regular employment and an increase in atypical forms of employment. Especially marginal part-time employment which is characterized by lower tax rates and lower social security contributions increased substantially after a reform in 2003 made this type of employment even more attractive to employers. In our paper we estimate the substitutability of regular employment by marginal part-time employment using data on the industry level before and after the reform. We detect high substitution elasticities with respect to three skill categories of regular employment in both time periods. The substitutability of unskilled full-time workers increased significantly after the reform.