1ST HUBBLE-SPACE-TELESCOPE OBSERVATIONS OF THE BRIGHTEST STARS IN THEVIRGO GALAXY M100=NGC-4321

As part of both the Early Release Observations from the Hubble Space T elescope and the Key Project on the Extragalactic Distance Scale, we h ave obtained multiwavelength BVR WFPC2 images for the face-on Virgo cl uster spiral galaxy M100 = NGC 4321. We report here preliminary resuls from those observations, in the form of a color-magnitude diagram for approximately 11,500 stars down to V approximately 27 mag and a lumin osity function for the brightest blue stars which is found to have a s lope of 0.7, in excellent agreement with previous results obtained for significantly nearer galaxies. With the increased resolution now avai lable using WFPC2, the number of galaxies in which we can directly mea sure Population I stars and thereby quantify the recent evolution, as well as test stellar evolution theory, has dramatically increased by a t least a factor of 100. Finally, we find that stars are present in M1 00 at the colors and luminosities expected for the brightest Cepheid v ariables in galaxies.