The purpose of this study was to examine empirically those who committed homicidal poisoning in Japan (N = 96). Typically, offenders were middle-aged (mean 43.2 years), had a fixed residence (99 percent), had no criminal record (81 percent), were employed (68 percent), and married (56 percent: 54 percent of the offenders were female. The offenders could be differentiated by categorical principal component analysis (CATPCA) into two poisoning themes: 'instrumental' (N = 65) and 'expressive' (N = 31). In 'instrumental' poisoning, the offenders were likely to induce a coma in a victim using medical supplies such as hypnotics, and then murder the victim, usually by strangling or stabbing. There were more co-offenders among 'instrumental' poisoners than among 'expressive' poisoners. The offenders who committed 'expressive' poisoning were inclined to poison victims serially or collectively in the workplace during daytime. These offenders were more likely to live with a parent/parents and exhibit mental health problems than those who committed 'instrumental' poisoning. (Published Abstract) Tables and references