The interstellar medium of early type galaxies has attracted a great deal of interest ever since Faber & Gallagher (1976) showed that a considerable amount of mass ejected by evolved stars could pile up over the lifetime of the galaxy (10^8 - 10^9 M[ scriptstyle sun ]). Surprisingly though, high resolution and sensitive HI observations demonstrated that in general much less gas is detected and that most of it seems to have been accreted (van Gorkom et al 1986; Wiklind & Henkel 1990). We have started a project, mapping a few early-type galaxies in detail, in order to shed light on the origin of the ISM in these objects.