The impact of biodiesel and new generation biofuels on emissions from heavy-duty diesel engines was investigated using a California Air Resources Board (CARB) certified diesel fuel as a base fuel. This study was performed on two heavy-duty diesel engines, a 2006 engine and a diesel particle filter (DPF) equipped 2007 engine, on an engine dynamometer over four different test cycles. Emissions from soy-based and animal-based biodiesel, renewable diesel fuel, and gas-to-liquid (GTL) diesel fuel were evaluated at blend levels ranging from 5 to 100%. Consistent with previous studies, particulate matter (PM), hydrocarbons (HC), and carbon monoxide (CO) emissions generally showed increasing reductions with increasing biodiesel and renewable/GTL diesel fuel blend levels for the non-DPF equipped engine. The levels of these reductions were generally comparable to those found in previous studies performed using more typical Federal diesel fuels. The DPF-equipped engine THC, CO, and PM emission levels were very low and did not show significant fuel impacts. Carbon dioxide (CO₂) emissions were slightly higher for biodiesel blends, and slightly lower for the renewable/GTL blends. Brake Specific Fuel Consumption (BSFC) was slightly higher for biodiesel and renewable/GTL blends, consistent with their lower energy density.