A detailed intralaboratory comparison of the determination of arsenic in complex wastewater samples by hydride generation and graphite furnace atomic absorption techniques has been conducted. Two hydride generation techniques were employed. One consisted of the use of sodium borohydride pellets and argon to sweep the arsine into a hydrogen flame. In the second, arsine was produced from a sodium borohydride solution and swept into an air-acetylene heated quartz tube. The hydride generation techniques yielded consistent, reliable data for highly complex wastewater matrices only when arsine generation was preceded by a closed acid digestion procedure. Complete recovery of arsenic (99%) was achieved using the graphite furnace technique and was found to be independent of the complexity of the wastewater matrix and of the organic form of arsenic present. Hydride generation and graphite furnace atomic absorption techniques were comparable with regard to sensitivity, reproducibility and relative detection limits, the latter was somewhat superior in terms of accuracy and the need for sample pretreatment. Both types of techniques are suitable for routine analysis.