The particulate contamination of five frequently prescribed drugs was studied. Samples were obtained in a laminar flow workbench according to millipore technique. The dry sample filters were examined with a binocular microscope at 50x and 100x. Particles were sized as to fibers, greater than 100 microns, 51 to 100 microns, 25 to 50 microns, and 10 to 24 microns. The results show the variability of contamination. Particulate counts appear to correlate with the manufacturing process. Bulk powders are highly contaminated, followed by lyophilize powders, then stable solutions. Until the clinical importance is resolved and manufacturing processes improved, in-line filters may be of value in selected patients.