  We present data on the modulation of the critical current with applied
magnetic field in UPt_3-Cu-Pb Josephson junctions and SQUIDs. The junctions
were fabricated on polished surfaces of UPt_3 single crystals. The shape of the
resulting diffraction patterns provides phase sensitive information on the
superconducting order parameter. Our corner junction data show asymmetric
patterns with respect to magnetic field, indicating a complex order parameter,
and both our junction and SQUID measurements point to a phase shift of Pi,
supporting the E_2u representation of the order parameter.
