Microalbuminuric [16] and macroalbuminuric [17] hypertensive insulin dependent diabetics were followed up for 4 years after the initiation of captopril therapy to assess the efficacy of ACE inhibitor therapy on albuminuria and blood pressure normalisation. Within the first six months of captopril therapy mean systolic blood pressure decreased in microalbuminuric and macroalbuminuric patients from 168.1 +/- 17.6 mmHg to 134.4 +/- 12.1 mmHg (19.2 +/- 7.1%) and from 177.6 +/- 16.8 mmHg to 143.5 +/- 12.7 (18.9 +/- 6.7%) mmHg, respectively. Mean diastolic blood pressure, similarly, showed a decrease from 91.9 +/- 9.1 mmHg to 74.4 +/- 10.3 mmHg (19.0 +/- 9.4%) in the microalbuminuric and from 95.3 +/- 13.7 mmHg to 78.2 +/- 7.3 (16.9 +/- 9.5%) mmHg in the macroalbuminuric group. After six months of captopril administration albumin excretion rates decreased as well, from 97.4 +/- 35.9 micrograms/min to 51.9 +/- 19.9 micrograms/min (46.9 +/- 7.6%) and from 766.7 +/- 577.9 micrograms/min to 365.1 +/- 298.4 micrograms/min (50.4 +/- 8.4%) in the micro- and macroalbuminuric groups, respectively. Thereafter, mean albumin excretion rates and blood pressure rose significantly, but at the end of the fourth year they were still significantly lower compared to that of the pretreatment period. After four years, albumin excretion rates were 71.3 +/- 29.6 micrograms/min in the microalbuminuric and 391.2 +/- 204.7 micrograms/min in the macroalbuminuric group. We conclude that ACE inhibitor therapy results in a rapid decrease of albuminuria and blood pressure, and despite a slow gradual increase, the albumin excretion rates and blood pressure values remain significantly lower than the initial values after four years.