Digit-symbol performance in methadone-treated ex-heroin addicts.

The digit-symbol substituion task (DSST) of the WAIS was given to working (MW) and nonworking (MNW) patients on high-dose methadone maintenance and to two comparison groups to assess the function of attention in these patients. Mean DSST scores were significantly lower for the MNW group than for the other three groups, which did not differ. However, the scores for the MNW group were within the normal range. DSST scores and lenght of methadon treatment (range: 11 months to 8 years) were positively correlated, providing no evidence of deterioration with increasing duration of treatment.