OBJECTIVES: The purpose of this study was to: 1) measure the incidence of prescription problems that require pharmacist intervention; 2) determine the types and relative frequency of prescription conveyance which contain problems that require pharmacist intervention; and 3) estimate the pharmacy personnel time and related practice expenses for prescriptions requiring intervention.  METHODS: This prospective study utilized an adaptation of the medication therapy intervention (MTI) data collection form.  Data were collected at two chain grocery store pharmacies by directly observing pharmacists for 3 weeks, during the hours of 9am to 6pm.  Information recorded with each intervention included the type of prescription, medication in question, reasons for intervention, intervention outcome, and time spent performing intervention.  Chi square analysis was conducted to compare percentage of intervention rates between prescription conveyances.  Kruskal-Wallis rank test was utilized to compare the time on task values for the interventions.  Poisson regression was used in order to determine if significant differences existed among the total number of interventions per group.  RESULTS: Pharmacists reviewed 1678 new prescriptions and intervened on 157 (9.4%) over a 13 day period.  A total of 12 hours and 11 minutes was required to perform all interventions for an overall average of 4.79 (SD=0.34) minutes per intervention.  Percentage of intervention rates between prescription conveyances was not statistically significant (p=0.21).  The time on task values for the interventions were also not statistically significant (p=0.39).  However, compared with handwritten interventions, e-prescribing interventions occurred 1.57 times less (p<0.0001), faxed interventions occurred 1.52 times less (p<0.0001), and verbal interventions occurred 2.05 times less frequently (p<0.001), on average.      CONCLUSIONS: E-prescribing interventions occurred less frequently compared with handwritten interventions, which may present a potential benefit.  Future efforts to develop and enhance e-prescribing are needed to add measurable value to patient care.