A field-study was carried out in Leticia (Amazonas department) in order to clarify the cause of death of a young man imprisoned in the municipal jail. After reviewing the clinical and epidemiological evidence, it was concluded that the cause of death was a heart attack, very probably caused by thiamine deficiency (wet beri-beri). Another four cases of mixed beri-beri were found amongst the prisoners, these having moderate manifestations, which had not been diagnosed. The diet given regularly to those incarcellated covered only half of the daily thiamine requirement for an adult population exposed to a tropical climate. This is the second report published recently in Colombia concerning beri-beri and should serve to tighten-up supervision of dietary control measures amongst high-risk populations, such as those confined to institutions.