A population based case-control study was conducted to determine whether risk of non-Hodgkin's lymphoma (NHL) in the absence of HIV infection is related to the previous use of tobacco, alcohol or recreational drugs. A total of 378 residents of Los Angeles County who were diagnosed with high- or intermediate-grade NHL were compared with individually age-, race- and sex-matched neighbourhood control subjects with regard to history of use of tobacco products, alcohol and ten specific recreational drugs. Risk of NHL among women decreased with increased consumption of alcoholic beverages (trend P = 0.03), with risk 50% lower among those consuming five or more drinks per week than among non-drinkers. Cocaine, amphetamines, Quaaludes and lysergic acid diethylamide (LSD) were each associated with a significantly increased risk of NHL in men with risk greater among those with more frequent use of these drugs. Confounding factors could not be excluded in these findings. The use of multiple types of drugs was also associated with a significantly increased risk of NHL in men (trend P = 0.005) with risk greatest among those using five or more types of drugs (odds ratio = 5.8, 95% confidence limits = 1.2-28.4); among these drugs, cocaine use appeared to account for the elevated risk of NHL among men based on multivariable analyses.