Abstract Deposition of radionuclides from the Chernobyl nuclear reactor in the Ukraine occurred over much of the United Kingdom. The magnitude of the deposition varied considerably, depending on the prevailing weather, but even in areas of low deposition, iodine-131, caesium-134 and caesium-137 were measurable on pasture and in cows' milk. The accident provided an opportunity to study the influence of differences in herd management and in climate upon transfer to cows' milk. In this paper, results from a small mixed farm in Cumbria are compared with those from a large dairy farm in Berkshire for the first few weeks after deposition. The contrasting herd management practices in operation at these farms result in very different temporal variations in activity concentrations in milk, although in neither case were the maximum concentrations in milk sufficient to warrant restrictions on distribution or consumption.