The usefulness of ionising radiation for the elimination of pathogenic bacteria in poultry meat has been well documented as have the e โ ects of this processing treatment on the nutritional status of the food, in particular, the vitamins. Unfortunately, much of the earlier research carried out on the e โ ect of irradiation on vitamins was carried out in solution or in model systems at doses much greater than those used commercially thereby resulting in considerable destruction of these compounds. Thus, those opposed to the process of food irradiation labelled the treated food as nutritionally poor. However, in reality, due to the complexity of food systems the e โ ects of irradiation on vitamins are generally not as marked and many processes, for example cooking, cause the same degree of change to the vitamins. Thiamin (vitamin is the most radi-B 1 ) ation sensitive of the water-soluble vitamins and is therefore a good indicator of the e โ ect of irradiation treatment. In this study the e โ ects of irradiation at either 4ยกC or [20ยกC followed by cooking on the thiamin content of chicken breast meat was determined. Results showed that whilst both irradiation and cooking resulted in a decrease in thiamin concentration, the losses incurred were unlikely to be of nutritional signiรcance and could be further minimised by irradiating the chicken meat at a low temperature. Thiamin analyses were carried out using high-performance liquid chromatography since this technique is faster and more selective than the chemical or microbiological methods more commonly employed. Total thiamin, both free and combined form, was determined following acid and enzyme hydrolysis.