The study involved the multivariate analysis of 3,961 death certificates that implicated heroin, morphine, and/or methadone. These data were obtained from the Office for National Statistics' drug-related poisoning mortality database for the years 1993 to 1998 for England and Wales. The data analysis determined the percentage increase in deaths by year by drug and the odds ratio (OR) of dying on the weekend from methadone-related overdose compared to dying from heroin/morphine overdose. The study found that from 1993 to 1998 annual opiate overdose deaths increased from 378 to 909. There was a 24.7-percent yearly increase in heroin deaths compared to a 9.4-percent increase for methadone-only deaths. This difference was significant after adjustment for sex, age group, polydrug use, area of residence, and underlying cause of death. The largest number of deaths occurred on Saturday (673). The OR of death from methadone overdose on Saturday and Sunday was 1.48 for methadone-only deaths compared to dying from heroin/morphine on the weekend, after adjustment for other covariates; however, the OR was not significant if the weekend was defined as Friday and Saturday. The study concluded that there was no evidence that the threefold increase in deaths over time was due to methadone. There was only equivocal support for the hypothesis that there was an excess of deaths from methadone on weekend. Thus, between 1993 and 1998, there has been a marked and dramatic threefold increase in opiate overdose deaths in England and Wales, but there is no evidence to support the contention that methadone is mainly responsible. The number of deaths attributed to heroin has increased at a significantly higher rate than those attributed to methadone. Some possible explanations for the increase in overdose deaths are discussed. 2 figures, 1 table, and 35 references