The paper describes tests on two typical designs of waste-oil space heaters, firing two different types of waste crankcase oils. Study results can be summarized according to the four substances investigated: particulates, polynuclear aromatic hydrocarbons (PAHs), organolead, and fuel samples. Analysis of samples from the air atomizing heater (AAH) confirmed previously identified elevated metal content of waste oil emissions. Bromine levels were exceptionally high. The ferrous ion (Fe(II)) content in particulate samples from the AAH was very low. Several PAHs were at elevated levels in gaseous emissions from both space heaters: the vaporizing pot heater (VPH) emissions had the higher PAH content. No organolead was detected in emissions from the AAH (organolead analyses were not performed on the VPH emissions). Mutagenicity assays of the particulate and the XAD samples from both heaters were mutagenic and contained direct-acting mutagens: emissions from the VPH were the more mutagenic. Comparison of the two types of fuels showed that emissions from the automobile waste crankcase oil were consistently more mutagenic than those from the truck waste crankcase oil.