The invention relates to a method of obtaining a desired protein from a transgenic host organism, the gene coding for this protein being not expressed until the host organism has been harvested and the method being characterized in that (a) the transgenic host organism contains the gene coding for the desired protein such that it is only expressed in the presence of a chemical inductor, and (b) contacting with the inductor takes place via the phase surrounding the host organism after the host organism has been harvested. The invention also relates to a host organism suitable for carrying out this method.