The occurrence of airborne Scots pine pollen was continuously monitored with Burkard traps at five locations situated along a 1000 kilometre transect in Finland during the ten-year period 1982–1991. The variation between years in airborne pollen dispersal was significant. The pollen season (defined as 10% of the cumulative pollen count for the year) began in South Finland, on average, on June 1st, and in North Finland 24 days later. The length of the mean local pollen season was 11 days, increasing towards the north. On average over 21% of the total pollen count of the year was caught on one single day. The temperature sums (d.d. >+5°C) required for the start of the pollen season decreased almost linearly from 193 d.d. in the south to 132 d.d. in the north. However, in several years the pollen seasons overlapped between sites at a distance of 500 km or more. The temperature sum on June 1st explained over 80% of the variation in the onset, median and end of the pollen season in Finland.