During the period 1978–1983 industrial hygiene consultants made 2185 ‘personal’ measurements of respirable dust throughout 35 Danish foundries. The mass of dust collected and the crystalline silica content were determined. Four-fold table analysis was used to evaluate the application of an exposure zone screening limit value (EZSLV), based on the gravimetric concentration alone, with the aim of reducing the number of samples requiring costly silica analysis. Factors for consideration were the relationships between EZSLV and the probability of false negatives, the probability of false positives and the predictive values. Various strategies for establishing the EZSLV are discussed. Restriction of silica analysis to samples that exceed the EZSLV reduces the analytical burden by 30% if a probability of 5%of false negatives is acceptable and by 20% if a probability of 1 % of false negatives is acceptable.