In the field experiments performed in 1999–2001 the profitability of late blight control in accordance with three decision support systems: NegFry, Simphyt and Stephan with routine fungicide program was compared. Potato protection carried out according to the recommendations of the decision support systems guaranteed higher profitability of late blight control than when potato was protected routinely. The highest profitability was recorded for susceptible variety Bekas protected according to NegFr.