  We found significant correlations between the arrival directions of the
highest energy photons (E>10 GeV) observed by EGRET and positions of the BL Lac
type objects (BL Lacs). The observed correlations imply that not less than
three per cent of extragalactic photons at these energies originate from BL
Lacs. Some of the correlating BL Lacs have no counterparts in the EGRET source
catalog, i.e. do not coincide with strong emitters of gamma-rays at lower
energy. The study of correlating BL Lacs suggests that they may form a subset
which is statistically different from the total BL Lac catalog; we argue that
they are prominent candidates for TeV gamma-ray sources. Our results
demonstrate that the analysis of positional correlations is a powerful approach
indispensable in cases when low statistics limits or even prohibits the
standard case-by-case identification.
