Of 39 silicotic sandblasters evaluated in 1972 and 1973, 17 (44 per cent) had positive serum antinuclear antibody reactions. This prevalence is higher than those reported for other pneumonconioses. Comparison of the groups positive and negative for antinuclear antibodies showed that patients positive for antinuclear antibodies were unlikely to have normal ventilatory function and were more likely to have roentgenograms showing large opacities. Both groups had similar proportions showing lobar cavitation or contraction.