The RFs of a quarter (3/12—2 complex, 1 simple) of area 19 cells tested for length selectivity, contained clear-cut silent strongly suppressive regions along the axis of optimal orientation. In these termed end-stopped cells, stimulation of suppressive regions resulted in ≥50% reduction in the number of spikes (see hypercomplex cells of Hubel and Wiesel, 1965; see also Dreher, 1972). The proportion of end-stopped cells in our sample is at the lower end of the range reported previously (25%–38%: Hubel and Wiesel, 1965; Duysens et al., 1982b; Rapaport et al., 1982; Pettigrew and Dreher, 1987; Tanaka et al., 1987; Guillemot et al., 1993; Tardif et al., 1997; Bergeron et al., 1998; Mimeault et al., 2002). However, in the present sample, inactivation did not have a clear effect on the presence and relative strength of suppressive regions of RFs.