We have conducted a survey of longitudinal magnetic fields (B/sub e/) among bright northern and southern Ap stars. The photoelectric technique used involves circular Zeeman polarimetry in the wings of H..beta... We find that the photoelectric B/sub e/ curves tend to be more harmonic than the photographic B/sub e/ curves. We have discovered magnetic fields in several rapidly rotating Ap stars. There is marginal statistical evidence to suggest that the rapid rotators might have surface magnetic fields smaller than the slow rotators; however, some very rapid rotators (P=0.5 days) can clearly have B/sub e/ extrema (approx.1 kilogauss) comparable to the extrema of slow rotators. We do not find serious evidence for irregular B/sub e/ variations, although we cannot exclude irregular variations of the order of 200 gauss in some stars. The astrophysical implications of our findings are briefly discussed. We have observed several Am and Hg-Mn stars, finding no evidence of magnetic fields.