Objective: To evaluate the concordance with criteria developed by the study investigators and supply costs associated with placement of i.v. lines and saline locks by paramedics in the out-of-hospital setting., Methods: This was a retrospective consecutive case series at an urban base hospital. Patients were treated by paramedics using one base hospital for medical control during December 1995. Base hospital written records and taped patient calls were reviewed to determine actual i.v. access method used by paramedics, chief complaint, and whether fluid administration was ordered. Indicated method of i.v. access was determined for each patient based on predetermined criteria developed by the investigators. i.v. access methods were ranked by cost of supplies as follows: i.v. line (i.v.) > saline lock (SL) > no i.v. line (No i.v.). An assignment of concordant treatment was made when actual = indicated method, discordant-overtreatment when actual > indicated, and discordant-undertreatment when actual < indicated., Results: 452 patients were treated via radio by the base hospital during the study period. 380 of 452 (84%) received an i.v.. 28 of 380 (7%) received fluid resuscitation in the field. 166 of 452 (37%) received concordant treatment; 253 (56%) discordant-overtreatment; and 33 (7%) discordant-undertreatment. Pediatric patients (< or =14 years of age) were more likely to be undertreated as compared with adults, 33% vs 3% (p < 0.001). Patients who had medical chief complaints were more likely to receive discordant-overtreatment as compared with patients who had trauma chief complaints, 61% vs 32% (p < 0.001). 73% of chest pain patients received discordant-overtreatment. Based on these data, the yearly cost of supplies used in i.v. access discordant-overtreatment was $13,735 for this base hospital and $560,000 for the Los Angeles County emergency medical services (EMS) system. 91% of the excess supply cost is due to patients' receiving an i.v. instead of a SL., Conclusion: Based on study criteria for utilization of i.v. lines vs SLs in the field, paramedics and base hospital personnel often provide discordant-overtreatment of patients by placement of an i.v. when a SL or No i.v. would suffice, resulting in unnecessary costs for EMS systems.