Plate assays for lipoxygenase producing microorganisms on agar plates have been developed. Both potassium iodide-starch and indamine dye formation methods were effective for detecting soybean lipoxygenase activity on agar plates. A positive result was also achieved using the β-carotene bleaching method, but the sensitivity of this method was lower than the other two methods. The potassium iodide-starch and indamine dye formation methods were also applied for detecting lipoxygenase production by Trichoderma reesei and Pichia pastoris transformants expressing the lipoxygenase gene of the fungus Gaeumannomyces graminis. In both cases lipoxygenase production in the transformants could be identified. For detection of the G. graminis lipoxygenase produced by Aspergillus nidulans the potassium iodide-starch method was successful. When Escherichia coli was grown on agar and soybean lipoxygenase was applied on the culture lipoxygenase activity could clearly be detected by the indamine dye formation method. This suggests that the method has potential for screening of metagenomic libraries in E. coli for lipoxygenase activity.