Objective was to quantify the chemical mechanisms of drug-induced lupus (DIL), and to make the data of different authors comparable between them. I have used seven assumptions as a starting point, based on empirical evidence; then an equation is drawn, describing the relationship between the quantity of the drug taken by the patient(s) and the probability of DIL appearance. The DIL-causing potential of each chemical group is a measurable intrinsic characteristic of that group, and the probability of DIL appearance is directly proportional to the total dosage of the drug in question. CONCLUSIONS: DIL is a syndrome that can be readily quantified and, as such, could be used as a model for idiopathic Systemic Lupus Erythematosus. On the other hand, the equation drawn here could be used to predict the lupus-inducing potential of many compounds that have not yet been studied. Other authors are encouraged to find similar equations in other drug-induced syndromes.