Samples of diluted bitumen (bitumen and diluent naphtha, 1:1, v/v) and coker distillate (coker gas oil and coker naphtha, 2:1, v/v) were obtained from Syncrude Canada Ltd. and subjected to column fractionation followed by biological testing of the fractions using the Salmonella/microsomal assay (Ames Test) and the Photobacterium phosphorium assay (Microtox test). The most significant toxicity (as measured with the Microtox test) was ascribable to fractions containing polycyclic aromatic nitrogen heterocyclic compounds (PANH); particularly basic-PANH. Significant mutagenicity (as measured with the Ames test) was also observed for the basic PANH fraction. Analysis of this fraction by gas chromatograph/high resolution mass spectrometry revealed the presence of alkyl-substituted polycyclic aromatic nitrogen heterocyclic compounds and alkyl-substituted quinolines. An analytical method was developed for the determination of basic-PANH in fish tissue. This method was applied to study of the uptake, elimination, and biotransformation of 6,7-dimethylquinoline and 6,8-dimethylquinoline by rainbow trout (Salmo gairdneri). Both compounds were readily bioconcentrated by fish from water and eliminated following exposure and depuration. The major metabolites of 6,7-dimethylquinoline were observed to be conjugated (sulfate or glucuronide) alcohols, whereas the major metabolites of 6,8-dimethylquinoline were observed to be conjugated (sulfate or glucuronide) phenols and an alcohol. Concentrations of the metabolites in bile, after exposure to approximately 1 mg/L of the dimethylquinolines in aquarium water, and 63 h of depuration with feeding, were observed to be 3 orders of magnitude above exposure levels. Twenty-one alkyl-substituted quinolines were subjected to toxicity testing using the Microtox test. The observed toxicity (expressed a 5-min EC$\sb{50}$) varied over two orders of magnitude from 0.30 mg/L to 30 mg/L depending upon the degree and nature of substitution. Dimethylquinolines substituted in the 2 positions were observed to be less toxic than those isomers without a 2-substituent. Dimethylquinolines involving 5 or 6 substitution together with a 3-substituent were observed to be most toxic. Three dimethylquinoline isomers were subjected to rainbow trout static fish bioassay. Results (expressed as 48h-LC$\sb{50}$) agreed with the observed 5-min EC$\sb{50}$ determined with the Microtox test.