In risk assessment, information from toxicity studies is combined with information on worker exposure. In general, agricultural practice implies long-term intermittent exposure to various pesticides. This issue can only be addressed when sufficient information exist, on exposure regimes. Patterns of application of pesticides and the use frequency of single pesticide products on a number of representative key crops from various agricultural sectors in the Netherlands were studied. The results show that there is an enormous variation in pesticide usage between and within sectors. On nearly all crops studied the number of applications with insecticides and fungicides was higher than the number of applications with herbicides. The average frequency of application of a the most used insecticide and fungicide products on the most intensively treated crops was between 10 and 20 times a year. But on most crops single pesticide products were used not more than seven times a year.