Real-time calibrated atomic emission spectroscopy in stack exhaust using a continuously sustained microwave plasma is under development for trace metals monitoring. The plasma, in a shorted waveguide attached to the stack by a short sample line, is powered at 1.5 kW, 2.45 GHz. An undiluted stack slipstream is isokinetically directed into the plasma at a nominal flow of 14 liters per minute. A pneumatic nebulizer attached to the sample line can momentarily, on command, inject a known concentration of metals solution providing a real-time calibration. Recent testing has been performed on the exhaust stack of an incinerator at the Environmental Protection Agency (EPA) National Risk Management Laboratory in Research Triangle Park. Three hazardous metals were monitored, lead, chromium, and beryllium. These measurements were referenced to EPA Method-29. A total of twenty spiked stack exhaust tests were carried out. Ten one-hour tests at high concentration (40 - 60 (mu) g/actual m3) and ten one and half-hour tests at low concentration (10 - 15 (mu) g/actual m3). The microwave plasma monitor achieved measurement accuracies of approximately 20% for lead and beryllium and 40% for chromium with a threshold detection capability of less than 3 (mu) g/actual m3 for a time response of approximately 1-minute. Laboratory work is continuing to add mercury, arsenic, and cadmium to the monitored metals.