Concentrations of Na, CI, Br and, l in aerosols and in inorganic gases were measured in the marine atmosphere off the west African coast (~0¿N; ~0¿W) in June 1977. During 8 days of the voyage, the meteorological situation was stable and well defined, and there was no precipitation, allowing a steady state analysis to be made of the mean rates of production and removal of the principal constituents of the system. Superimposed on these mean fluxes, strong diurnal fluctuations in the concentrations of Br and I (but not Na or Cl) were observed. Daytime concentrations of gaseous inorganic Br and I were about double their nighttime values. During this same period, the daytime concentrations of particulate Br were about half their nightime values, while particulate I concentrations showed only small, uncorrelated variations. Analysis of these results suggests that there may be a reversible, day-night exchange of Br between the particulate and gas phases; for I it is speculated that at night an appreciable fraction of the gaseous inorganic I present existed in a form not efficiently trapped by the LiOH-impregnated filters of our sampling apparatus.