The Isoparaffins covered in this manuscript are branched aliphatic hydrocarbons with a carbon skeleton length ranging from approximately C10 to C15. They are used in the manufacture of liquid imaging toners, paint formulations, charcoal lighter fluid, furniture polishes and floor clearners. Potential exposure exists in the petroleum, printing and paint industries. Isoparaffins have a very low order of acute toxicity, being practically non-toxic by oral, dermal and inhalation routes. However, aspiration of liquid isoparaffins into the lungs during oral ingestion could result in severe pulmonary injury. Dermally, isoparaffins have produced slight to moderate irritation in animals and humans under occluded patch conditions where evaporation cannot freely occur. However, they are not irritating in non-occluded tests, which are a more realistic simulation of human exposure. They have not been found to be sensitizers in guinea pig or human patch testing. However, occasional rare idiosyncratic sensitization reactions in humans have been reported. Instillation of isoparaffins into rabbit eyes produces only slight irritation. Several studies have evaluated sensory irritation in laboratory animals or odor or sensory response in humans. When evaluated by a standard procedure to assess upper airway irritation, isoparaffins did not produce sensory irritation in mice exposed to up to 400 ppm isoparaffin in air. Human volunteers were exposed for six hours to 100 ppm isoparaffin. The subjects were given a self-administered questionnaire to evaluate symptoms, which included dryness of the mucous membranes, loss of appetite, nausea, vomiting, diarrhea, fatigue, headache, dizziness, feeling of inebriation, visual disturbances, tremor, muscular weakness, impairment of coordination or paresthesia. No symptoms associated with solvent exposure were observed.(ABSTRACT TRUNCATED AT 250 WORDS)