Section headings and selected papers: Preface. Plasma Densities. International Reference Ionosphere - plasma densities: status 1988, K Rawer & D Bilitza; Aeronomical calculations of valley size in the ionosphere, J E Titheridge. Ionospheric characteristics for IRI in real time, B W Reinisch et al . Mapping. Longitude features shown by topside sounder data and their importance in ionospheric mapping, N P Benkova et al . Ionospheric mapping using satellite data of natural HF noise, S A Pulinets et al . Atmospheric gravity waves and ionospheric modelling, Lj R Chander et al . Plasma Temperatures. Solar activity variation of ionospheric plasma temperatures, D Bilitza & W R Hoegy; Comparison of ionospheric electron temperature rocket measurements over Natal, Brazil with the IRI model, I J Kantor et al . Ionic Composition and Drifts. Variations of helium ion density from theoretical considerations, R Koleva & I Kutiev.; Applications of IRI. Ionospheric and tropospheric path delay obtained from GPS integrated phase, incoherent scatter and refractometer data and from IRI-86, A J Coster et al . Data Handling. Structure and information flows in the distributed solar-terrestrial physics data base system, C C Abston et al . URSI Working Group G-4 on Ionospheric Informatics. N(h) profile data at world data centers, J H Allen et al . Discussion of the valley problem in N(h) analysis of ionograms, T L Gulyaeva et al . Author index.