This analytical method is a validated measurement procedure for the determination of quartz [14808-60-7] and cristobalite [14464-46-1] in workplace air after personal or stationary sampling. Sampling is performed by drawing a defined volume of air through a particle filter using a suitable flow-regulated pump. After gravimetric determination, the respirable fraction of quartz or cristobalite retained on the filter is analysed by an X-ray diffractometer. The relative limits of quantification (LOQ) are for a sampling period of two hours with air sampling volumes of 0.24 to 45 m³ for quartz 0.0040 to 0.38 mg/ m³ and for cristobalite 0.0020 to 0.19 mg/m³. For a sampling period of eight hours the LOQ are between 0.0010 and 0.094 mg/m³ and between 0.0005 and 0.047 mg/m³, respectively. The expanded uncertainty is 28% for 0.075 mg/m³ of quartz and is estimated to be lower for cristobalite. This analytical method has been accredited by the accident insurance companies for the detection in workplace air of substances that are carcinogenic, mutagenic or toxic to reproduction. This method has been tested and recommended for the determination of quartz and cristobalite in work areas by the German Social Accident Insurance (DGUV). Both personal and stationary sampling can be performed for measurements in order to evaluate work areas.