We performed a retrospective study to determine whether the use of a nomogram in General Medicine Wards is superior to the empiric method for the adjustment of heparin dosage. In the period october 1998-september 1999 we treated 138 patients with continuous infusion of heparin using a weight-based nomogram. Then we compared these data (nomogram group) with data from period october 1997-september 1998, when we had treated 155 patients with heparin, using empiric method for dose adjustments (empiric group). The proportion of patients reaching the therapeutic aPTT 24 hours after the start of therapy was 90.5% in nomogram group compared with 56.1% in the empiric group (P < 0.001). The proportion of nontherapeutic and subtherapeutic aPTT was significantly reduced in the nomogram group (6.0% vs. 11.1%, P < 0.001; 13.7% vs. 19.3%, P < 0.001). Furthermore, in the nomogram group the proportion of consecutive nontherapeutic or overtherapeutic values were significantly reduced (0.1% vs. 2.2%, P < 0.001; 1.8% vs. 2.3%, P < 0.001). We conclude that a weight-based heparin nomogram adapted for own aPTT range is successfully used in General Medical Wards of a community hospital.