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Very high energy gamma ray emission from the blazar Markarian 421 has repeatedly been detected with the Whipple 10 meter imaging Cherenkov telescope. During observations made between December 1993 and April 1994, the integrated photon flux was about a factor of two below that of two previous observation periods in 1992 and 1993. On May 14th, 1994, a significant increase was observed which reached a level of $2.1\pm0.3\times 10^{-10} cm^{-2} s^{-1}$ above 250 GeV during the following day. Because of the moon, further observations were delayed until June 1st when Markarian 421 was again observed at a level comparable to the low state of winter and spring 1994. This is the first evidence for short time variability in the gamma ray emission above 100 GeV. Within 24 hours of this observation an increase in the X-ray emission by a factor of 2 was detected by the ASCA X-ray satellite. The observations add important clues to our understanding of the particle acceleration and formation of relativistic jets in blazars.
