Varieties of Guaymí bean and the MUS 181 line were evaluated in five locations in Costa Rica, in five plant populations (140.000; 170.000; 200.000; 230.000 and 260.000 plants per hectare). Some plants were sprayed with benomyl 50PM fungicide at 0.35 kg per hectare, while others did not receive such treatment. Yield losses caused by pathogenic agents were determined, and an economic analysis of the treatment was performed. A low incidence of Mustia Hilachosa/bean diseases was reported on treated plants. Plant populations of 140.000 and 170.000 plants per hectare produced the greatest profit and the highest marginal return rateo