Track Name: Ice nucleus concentrations measured at latitude 78S with a mixing cold chamber from 1 December 1961 to 10 February 1962 were found to be as high as or higher than those measured in sub-tropical latitudes in the southern hemisphere at the same season with similar equipment. From the way in which the number of active ice nuclei depends upon the temperature it is deduced that the nuclei effective above about −26C are predominantly in the size range 0.02μ to 0.2μ in diameter. The concentrations varied over a similar range to those in low latitudes but fluctuations were generally more orderly and less abrupt than elsewhere, and the nuclei appeared to be more thoroughly mixed with the air than is usually the case. Consoles: B 29/100