The total insulin dosage and its distribution throughout the day were evaluated in newly diagnosed Spanish IDDM patients treated with semisynthetic human insulin. We assessed the insulin dosage and its distribution modifications related to an inpatient versus outpatient setting. We compared our results with classical theoretical algorithms based on patients treated with animal insulin and with alimentary habits which differ from our geographical area. The initial total daily dose (0.68 +/- 0.27 U/kg per day) did not substantially differ from the usual recommended dose (0.70-0.80 U/kg per day). A substantial decrease in total insulin dose was observed in ambulatory patients (0.55 U/kg per day). The reduction in dosage when we substituted regular insulin for intermediate acting insulin was smaller than what is commonly advised. A very low proportion of patients needed to add extra regular insulin to the pre-dinner intermediate insulin dose to achieve acceptable glucose control. Moreover, in these cases regular insulin comprised only 10% of total daily dosage, a proportion clearly inferior to that recommended. The majority of this group of patients needing regular insulin plus intermediate insulin at pre-dinner were treated with human zinc insulin. Most of our patients were acceptably controlled with a regular insulin dose before breakfast and lunch and an intermediate dose before dinner. Finally, human insulin pharmacokinetics plus our Mediterranean alimentary habits might be the explanation to our findings.