The author responds to comments by Knowlton J. Caplan (NIOSH- 00237112) on his article entitled, Silica Exposure in Hand Grinding Steel Castings (American Industrial Hygiene Association Journal, Vol. 53, No. 1, pages 42-48; see NIOSH-00204981). The previously published article reported on air quality control and employee exposures to silica (14808607) during the hand grinding of steel castings. The letter to the editor that the author is responding to describes two 'fatal flaws' involving the recommendations in the original report regarding the filter/recirculation system being studied. The author of the letter took exception to recommendations in the original article that filters in downdraft benches be upgraded or that they be connected to a central dust collector and exhausted to the outside. In response to the criticisms, one of the authors of the original study agreed that a properly engineered filter/recirculation system would be successful in controlling dust in such operations but emphasized the larger issue of the efficacy of the practice of recirculating silica contaminated air, particularly in light of an American Conference of Industrial Hygienists publication and another study, both of which indicated that such systems are incorrectly operated or poorly maintained resulting in inadequate air quality. The author of the original study also addressed concerns expressed by the author of the letter regarding the relationship of the discharged filtered air to the work station.