An aircraft measurement program was undertaken in the savanna regions of central South America in the dry season of 1980 to investigate the atmospheric effects of large-scale biomass burning. The smoke from the fires was found to be largely confined within an approximately 3-km-deep boundary layer capped by a subsidence invrsion or a stable layer. This condition typically persists for week-long periods as a result of the synoptic subsidence occurring during the dry season. Photochemical production of ozone occurred in the polluted layer over the entire Cerrado region of central Brazil. The factors controlling the concentration of this ozone are examined, and an estimate of the amount of ozone produced is reported.