Diesel engines are a significant source of nitrogen oxides (NOx) and particulate matter (PM) which may cause adverse health effects on the cardiovascular and pulmonary systems. There is little consistency between many studies to establish which engine parameter is a key factor to determine the toxicity of diesel exhaust. The aim of this study was to correlate engine operating systems with cytotoxicity using human cells. A dynamic direct exposure system containing human cells grown at the air liquid interface (ALI) was employed to expose human derived cells to diesel exhaust emitted under a range of engine loads. To determine correlation between engine load and cytotoxicity, concentrations of NOx and carbon (organic and elemental) were measured. Comparison between filtered and unfiltered exhaust was also made. To assess cytotoxicity and determine mechanisms responsible for toxic effects, various bioassays measuring a range of endpoints were used including: cell metabolism (MTS), cell energy production (ATP) and cell lysosome integrity (NRU). The human cells selected in this study were lung (A549) and liver (HepG2) derived cells to detect if observed cytotoxicity was basal (i.e. affect all cell types) or organ-specific. Results showed that NOx gas concentrations increased as engine load increased which resulted in significant cytotoxicity to both A549 and HepG2 cells. In contrast carbon measurements remained relatively constant across loads with no observable significant difference in cytotoxicity by filtering diesel exhaust. This result suggests that the gaseous component of diesel exhaust may contribute higher cytotoxicity than the particulate component. Post exposure incubation was an important factor to consider as only gaseous components of diesel exhaust exhibited observable immediate effects. Our findings suggest engine torque as a reliable indicator of cytotoxicity on human cells. The advantages of the dynamic direct exposure method include a more realistic representation of human respiratory toxicity and modularity which would allow for the analyses of pollution other than diesel exhaust.