The potential acute toxicity of a ribozyme (ANGIOZYME™) targeting theflt-1 vascular endothelial growth factor (VEGF) receptor mRNA was evaluated in cynomolgus monkeys following i.v. infusion or s.c. injection. ANGIOZYME was administered as a 4-hour i.V. infusion at doses of 10,30, or 100 mg/kg or a s.c. bolus at 100 mg/kg. End points included blood pressure, electrocardiogram (ECG), clinical chemistry, hematology, complement factors, coagulation parameters, and ribozyme plasma concentrations. ANGIOZYME was well tolerated, with no drug-associated morbidity or mortality. There was no clear evidence of ANGIOZYME-related adverse effects in this study. Slight increases in spleen weight and lymphoid hyperplasia were observed in several animals. However, these changes were not dose dependent. Steady-state concentrations of ANGIOZYME were achieved during the 4-hour infusion of 10,30, or 100 mg/kg. Dose-dependent elimination of ANGIOZYME was observed, with faster clearance at the two highest doses. ANGIOZYME was slowly absorbed after s.c. administration, resulting in steady-state concentrations for the 9-hour sampling period. Monkeys in this toxicology study received significant plasma ANGIOZYME exposure by both the s.c. and i.v. routes.