We tested a modified Beilstein method for detecting pyrethroids on bednets under laboratory conditions using an emulsifiable concentrate of permethrin (50 EC) for viability as a simple standardized field test and to judge its reliability for detecting different insecticide doses. At the recommended doses of permethrin(0.5 g/m2), sensitivity was near 100%, even when small pieces of fabric were tested and time of extraction was limited. In unwashed nets sensitivity stayed high (80–95%) down to 0.1 g active ingredient/m2. In untreated nets false positives were rare (0–2%). The test could become a valuable tool in vector control programmes: it is cheap, easy to learn and to perform. The Lot Quality Assurance Sampling method, using an upper and lower performance threshold, could be applied for monitoring the impregnation campaigns.