The six Avicel products designed for compression - the classical grades PH-105, PH-103, PH-101 and PH-102, and the new Avicels PH-112 and PH-200 - have been submitted to a comparative investigation for both their basic and tableting properties. According to the manufacturer all these products differ by their nominal particle size and moisture content. Basic properties of the powders were first determined, namely moisture content (loss on drying and Karl Fischer titration), particle size and shape (sieving and image analysis), densities (true bulk and tap densities, Hausner ratio) and flow properties (vibratory hopper technique). As tableting properties, the compactibility of the powders and the effect of adding a hydrophobic lubricant (0.5% magnesium stearate) on the compact strength were evaluated by preparing compacts at a given applied pressure using a hydraulic press. Weight and dimensional variations were assessed by preparing tablets at a target crushing strength of 70 Newtons on a high speed machine. The comparison of the conventional Avicel PH grades showed that Avicel PH-105 differed markedly in its properties (high compressibility on tapping, high compactibility, inacceptable tablet weight variability and very poor disintegrating properties) from the other grades. As to the two new Avicel PH grades, conflicting results with the literature were obtained with the low-moisture product Avicel PH-112. We observed, like other authors but in contrast to manufacturer's data, values of compactibility and strength reduction ratio upon lubrication as well as of the coefficient of tablet weight variation similar to those of the standard Avicel PH-102, of comparable particle size. This can be certainly explained by an uptake of moisture of the Avicel PH-112 powder as proved experimentally. This would limit the use of this material to an air-conditioned room. The large particle size product Avicel PH-200 displayed a compactibility close to that of all the other Avicel PH grades (except PH-105), but the highest susceptibility to magnesium stearate. As expected, because it is free-flowing, Avicel PH-200 gave the lowest tablet weight variability. Additionnally, the two new grades showed disintegrating properties similar to those of Avicel PH-103, PH-102 and PH-101. Finally, one should bear in mind that the small differences reported here may not be significant because of substantial inter batch variability.