In situ measurements of daytime equatorial ionospheric E and F region electron densities were carried out using a high-frequency capacitance probe on board a SONDA III rocket launched from Natal, Brazil, on July 26, 1984. Wave structures in the electron density profile having a scale length of ~1.5 km to ~10 km and amplitude of ~10 percent of the ambient density were detected during the downleg trajectory. Possible sources of these waves are discussed, and their possible implication for irregularity formation under nighttime conditions is briefly mentioned. ¿ Americal Geophysical Union 1988