In May 1975, a sequence of rocket and balloon experiments was launched from Chilca Base, Peru (12.5°S, 76.8°W, Dip = −0.7°) as part of a program called Operation Antarqui. Detailed analysis and comparison of the data have yielded a significant and unexpected result, namely the first direct measurement of lower mesospheric response to a galactic X-ray source. This result could only have been determined at the equator, where cosmic ray background effects are minimal. Our objective was to seek out the equatorial energetic electron belt, sporadically reported to have fluxes approaching auroral levels, measure the X-ray bremsstrahlung radiation produced by this particle belt, and determine the influence of this radiation on the mesosphere and stratosphere. High altitude rockets were used to measure electron and X-ray fluxes, while near simultaneous samplings of O 3, conductivity and meteorological parameters were conducted in the lower atmosphere. In addition, monitoring of cosmic rays and energetic X-rays near 40 km was made with balloon-borne instrumentation. The results show no trace of unusual electron fluxes up to 335 km but do show a strong enhancement of X-rays between an early and late night comparison on 23–24 May. This X-ray enhancement has been found to be consistent with the observed doubling of the conductivity (and hence ionization) near 65 km. The conductivity increase cannot be explained by any other known source. Preliminary attempts to identify the X-ray source currently favor Sco X-1 as the primary source of X-ray enhancement. This conclusion is consistent with the known position of Sco X-1 for each of the two measurements, and with the energy spectrum of the observed radiation vs that of Sco X-1. A power spectrum analysis of the X-ray data has further shown a periodicity of intensity in phase with the payload coning period, which further verifies the point source origin of the X-rays. This analysis demonstrates that stellar X-ray sources can have measurable influence on lower mesospheric ionization. It also shows that the equatorial energetic electron belt is not a permanent feature of the region.