Lyophilized pellets, suitable for use in a microfluidic device, and a method for preparing the same are described. The lyophilized pellets contain various biological reagents, or microparticles, and a cryoprotectant. The lyophilized pellets have a high degree of sphericity and are in the size range 0.5 to 35 .mu.L. The pellets are prepared by dispensing drops of reagent solution on to a cryogenically cooled plate, followed by subjecting to a vacuum.