The specificity and sensitivity of four visualization reagents, ninhydrin, o-phthalaldehyde (OPT), fluorescamine and o-diacetylbenzene (DAB), for the detection of histamine on thin-layer chromatograms developed in several optimal solvent systems were compared. While the ninhydrin reagent is the most sensitive with a detection limit of 0.4 nmoles of histamine, the DAB and fluorescamine reagents offer the most potential as histamine-specific visualization reagents. The OPT reagent was unsatisfactory because the fluorescent sports developed with this reagent were unstable. Of 19 amines tested in addition to histamine, ninhydrine reacted with 17, fluorescamine with 8 and DAB with 15. Since only histidyl-leucine, octopamine, serotonin and tryptophan interfere in the resolution of histamine in any of the solvent systems used, DAB provides some advantages by not reacting with histidyl-leucine. In addition, with the acetone-ammonia (95:5) solvent system, which adequately separates histamine from all other tested amines, no background interference problems were noted when using DAB as the visualization reagent. Background interference problems with the acetone-ammonia system were evident with the other visualization reagents. The sensitivity of the DAB and fluorescamine methods (4 nmoles of histamine) allows both reagents to act as semi-quantitative screening agents for potentially toxic levels of histamine in food extracts. With a variety of food samples, DAB visualization following development in acetone-ammonia (95:5) was the optimal thin-layer chromatographic method.