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professions of restricted admission, extensive training, and punishment mistakes still happen. Our studies of errors involving health

drug names indicate that these mistakes may be related more to the organisation of memory and the processing of information than to laziness or negligence. A practitioner’s memory appears to be organised so that typical or familiar drug names are centrally located and easily accessed; then familiar objects may be recognised without using conscious attentionThus a less familiar drug name (’Losec’ when it came onto the market) is likely to be recognised as the more familiar ’Lasix’, as happened in the case reported by Dr Faber and colleagues (May 25, p 1287). We reviewed reports of wrong drug dispensing errors by pharmacists and concluded that the mistakes were unlikely to be due to chance and could be caused by the organisation of memory. Reports published between 1977 and 1987 totalled 52. We designated drug products reported to be in the top 200 drugs prescribed each year as familiar and other drugs as unfamiliar. We then assigned each reported error to one of four classes: a familiar drug substituted for a familiar drug (n = 11), a familiar drug substituted for an unfamiliar one (n = 19), an unfamiliar substituted for a familiar drug (n =1 ), and an unfamiliar drug substituted for an unfamiliar drug (n=21). The distribution was significantly different from that predicted by chance (=364, p