We report here the results of studies documenting the contamination of a cigarette-appearing smoking article labeled Eclipse with glass fibers, fragments, and particles. Eclipse, a product of the R. J. Reynolds Tobacco Company (RJR), was commercialized in June of 1996. Eclipse is unlike conventional cigarettes in that, like its predecessor Premier, it is designed to heat and not burn tobacco. The purpose of Eclipse was to simplify the chemical composition and reduce the biological activity of the mainstream and sidestream smoke and to achieve a significant reduction of environmental tobacco smoke. In Eclipse, tobacco pyrolysis is reduced by a carbon fuel rod that serves as a heat source for generating an aerosol having nicotine and tobacco flavor. The carbon rod, at the tip of the cigarette, is insulated and bound with two wrapping mats of glass fibers. Recently, Eclipse has been modified to address consumer complaints of burdensome draw and off-taste. The redesigned Eclipse, which we have termed the NEW Eclipse, has an unconventional filter-appearing mouthpiece that consists of a cellulose acetate cylindrical bundle with a central hollow tunnel. In our analysis of Eclipse, glass fibers (length:width aspect ratio, > or = 3:1) were: (a) observed protruding from the tip; (b) identified on the white cigarette wrapping paper; (c) viewed on the surface of the cork-appearing tipping paper; (d) found in the pack residue; (e) discovered lying freely on the cut surface of the filter by both light and electron microscopy; (f) harvested from the filter with adhesive tape; and (g) displaced when Eclipse was smoked mechanically. In a study of Eclipse that had not been removed from carefully opened packs, we observed that > or = 95% of the filters were contaminated with glass fibers (Eclipse: Regular, n = 114/120, 95%; Milds, n = 118/120, 98%; Menthol, n = 120/120, 100%). Likewise, 99% of NEW Eclipse had glass fibers on the redesigned filter (Regular, n = 119/120). In contrast, glass fibers were never observed on the filters of conventional United States filter cigarettes that had been used as controls (n = 0/120, 0%). In a study of Eclipse (n = 60), the number of glass fibers contaminating the filter surface ranged from 5 to 55. Glass fibers as well as fiber fracture items [aspect ratio, < 3:1 (e.g., particles, fragments, bits, chips, flakes, specks, and dust)] were discovered in the pack residue. The average number of glass fibers in the residue of a pack of Eclipse was 7,548 (SE +/- 3443; range, 1,164 to 26,725 glass fibers/pack; n = 7 packs). The thin and fragile glass fibers of the insulation mats had most likely been broken and fragmented in the high-speed multiple-step Eclipse manufacturing operation. Invariably, puffing on Eclipse discharged glass fibers and glass particles from the filter into the smoker's mouth. Subsequently, the bioresistant glass fibers and microscopic glass dust are inhaled and/or ingested. Contamination of Eclipse filters with glass fibers and glass dust poses a potential and unnecessary health hazard to uninformed consumers. Eclipse is a paradigm of the health danger that may be imposed by technically complex tobacco articles and nicotine delivery devices promoted by an unregulated industry to smokers worldwide, many of whom are addicted to nicotine and who seek a less hazardous cigarette.