Gamma-ray observations of BL Lac objects

We present results from observations of a sample of BL Lac objects by the COMPTEL and EGRET experiments aboard the Compton Gamma-Ray Observatory in 1993-94. The main targets in the sample were selected on the basis of their X-ray brightness and apparent spectral hardening at hard X-ray energies. One of the targets, PKS 0521-365, was detected by EGRET and these data are presented along with results from contemporaneous ground-based monitoring at radio wavelengths. Subsequent X-ray observations of this unusual source by ASCA demonstrate clearly that, although originally classified as a BL Lac, it is in fact better descibed as a flat spectrum radio quasar at the present epoch. None of the remaining sources in the sample were detected, by either COMPTEL and/or EGRET. Upper limits on the γ-ray flux from all the non-detected BL Lacs are presented.