The grass pollen content of the air at four sites bordering the Bristol Channel (at Bristol, Cardiff, Penarth and Penmaen) was studied. The trap at Penmaen was situated at an official climatological station which provided the meteorological data used in the surveys. Although at certain times large differences could be seen between the concentrations of grass pollen at the different sites, overall the findings for the four sites were similar. Changes in the atmospheric pollen concentration related to variations in meteorological conditions. At the peak of the season high concentrations of grass pollen persisted throughout the night.