Solar X-ray bursts observed by a proportional counter carried on the IMP-F satellite have been analysed for correlation with optical Hα flares and radio bursts. The solar X-ray flux at energies greater than 3 keV was measured each 82 seconds and consisted of impulsive bursts superimposed on a slowly varying X-ray background. During June and July 1967 there were an average of ~10 bursts per day with intensities greater than 400 photons cm−2 s−1 (2 × 10−6 erg cm−2 s−1) which was the threshold for observation of a burst.