AbstractThe winter activity of soil organisms and of the fungusPhacidium infestansinoculated on excised Scots pine shoots was monitored by measuring CO2concentrations under the snow cover. Other variables measured, relating to respiration, were the temperature under the shoot heaps and the depth of snow cover. The concentrations were highest when the temperature under the snow remained at a relatively high level during the whole winter which also favoured respiration fromP. infestans. When the soil was covered with a thin layer of snow, the conditions did not favor a high respiration rate until the snow melt period.