A detailed description and analysis is presented of the Lagopedo II results. The rocket was launched on September 11, 1977. Prior to an explosive chemical release a rocket-borne ion mass spectrometer and dual-frequency beacon measured the ion composition and electron content of the undisturbed F region above Kauai, Hawaii. These results are compared to a detailed calculation of ionospheric ion denities. Considerable H2O outgassing produced measurable 18+(H2O+) and 19+(H3O+) currents which together with O+ current were used to determine the H3O+/H2O+ dissociative recombination rate ratio. The explosive event at 283 km swept clean a l-km-radius region. The boundary of the ionic void was characterized by a steep gradient in the ion density. Results for the first 60 s after the event are presented which show changes in ambient ion species 14+, 16+, 30+, new reactant species 15+, 17+, 18+, 19+, 27+, and 46+, and evidence of ionic depletion by sweeping.