This study was conducted to determine whether loop diuretics are more effective than placebo in reducing blood pressure without raising serum lipid levels, and whether bumetanide is more effective than furosemide in this respect. In a double-blind, 24-week placebo-controlled crossover study, 27 patients with essential hypertension were treated in four periods of 6 weeks each, including placebo twice, furosemide 40 mg daily, and bumetanide 1 mg daily. Several metabolic parameters, including serum lipid levels, and blood pressure were assessed. Overall levels of total cholesterol, triglycerides, and low-density lipoprotein (LDL) cholesterol were 5%, 12.4%, and 4.8% higher, respectively, during loop diuretic therapy than during placebo treatment. Overall systolic and diastolic blood pressure measurements were 12 mmHg and 4 mmHg lower, respectively, during loop diuretic therapy than during placebo treatment. Any added effect of bumetanide on serum lipid levels and blood pressure compared with furosemide, however, could not be confirmed. Our results indicate that the loop diuretics bumetanide and furosemide are effective in reducing blood pressure, and influence serum lipid levels markedly less than do thiazide diuretics or chlorthalidone. In addition, these results indicate that differences in blood pressure reduction and serum lipid levels between the two compounds were small and nonsignificant.