A method to obtain accurate dissolved oxygen concentration (DO) measurements within a 16-mm microzone was developed using oxygen-permeable dialysis tubing with a 12-ml water sample and a modification of the micro-Winkler technique. Controlled experiments showed that W within tubes reached 99% equilibrium with ambient water in less than 3 hours in lotic waters and in less than 5 hours in lentic waters with experimental error of 0.05 mg/liter. A kit to perform the DO measures can be assembled for about $150, and samples can be run in less than 10 minutes.