By using suitably marked X-chromosomes it was possible, on the one hand, to distinguish between induced mitotic recombination in euchromatin and in heterochromatin and, on the other hand, to get some ideas about the distribution of the recombination events within the euchromatin. These results have been taken as a basis for discussing the question: To what extent is induced mitotic recombination a simple breakage-fusion mechanism and to what extent is it comparable to meiotic recombination? Furthermore, the results give evidence that must be considered when recombination data are used to make mitotic maps.