An attempt is made to forecast the start, the peak and the end of the pollen season. The cumulated activity method, a development of the temperature sum method, is used. Temperature (T) is transformed to activity (A) by the formula A = 2** ((T+g)/(10+h))-k where g, h and k are parameters (** indicates exponentiation). The method is tested using pollen and weather measurements from Stockholm for the years 1973–88. Of the eight pollen types tested, the best results are gained forUlmus, BetulaandPinus, with a prediction precision varying between three and six days. The method was less relevant forAlnusandQuercusand not satisfactory forCorylus, Poaceae andArtemisia.