Sepracell-MN has provided a simple, rapid means of isolating peripheral blood monocytes. However this product is no longer available. Consequentially we have developed a Percoll gradient which matches Sepracell-MN in simplicity and yield of monocytes. Using this Percoll gradient, an average of 7 x 10(6) monocytes with a purity of 83% were obtained from 30-40 ml of blood. These monocytes were at least 97% viable and responded to chemotactic stimuli in comparable numbers to those prepared using Sepracell-MN