  Using the RXTE PCA we discovered dips in the X-ray light curves of the
black-hole candidate GRO J1655-40 during outburst. They are short (~minute) and
deep (down to ~8% of the out-of-dip intensity). Similar kind of dips were found
in 90s measurements of the RXTE ASM during the same outburst. The occurrences
of the dips are consistent with the optically determined orbital period, and
were found between photometric orbital phases 0.72 and 0.86. This constitutes
the first evidence for orbital variations in X-rays for GRO J1655-40. The PCA
data indicate that an absorbing medium is responsible for these dips. Using
these results we are able constrain the extent of the absorbing medium and the
central X-ray source. GRO J1655-40 was in the canonical high state during our
PCA observations.
