This document summarizes a study on pesticide residues in onions in Isfahan, Iran. The study tested different extraction methods to measure residues of the pesticide Profenofos used to control onion thrips. Liquid-liquid extraction recovered residues at 117% on average but was inefficient. Solid phase extraction recovered only 39.5% of residues on average. Solid phase microextraction recovered between 40.8-106% of residues on average. The study found that 33% of onion samples contained pesticide residues above Codex limits, indicating inaccurate application of Profenofos by some farmers in the pre-harvest period. The study concludes accurate measurement of pesticide residues is important to ensure data quality and pesticide use