Effects of methylene chloride (CH2Cl2) on blood pressure (BP), body weight, plasma renin activity, hepatic histological structure of spontaneously hypertensive rats (SHRs) and normotensive control rats (NCRs) were studied. Administration of 0.15 mL/100 g/day CH2Cl2 to SHRs for five days reduced the BP from 172 +/- 7 mm Hg (mean +/- SEM) to 155 +/- 6 mm Hg without changing the plasma renin activity. The same regimen did not change the BP of NCRs. A weekly injection of 0.15 mL/100 g/day of CH2Cl2 for five consecutive weeks failed to significantly alter the BP of either SHRs or NCRs. The polyhalogen, whether administered daily or weekly, did not affect the body weight of either SHRs or NCRs. Administration of CH2Cl2 daily for five days produced an extensive but reversible hepatic centrolobular loss of glycogen in both SHRs and NCRs. No other changes were observed in the livers.