The effects of dissolved humic materials (DHM) on the photoinduced toxicity of fluoranthene to juvenile fathead minnows (Pimephales promelas) were studied in single-treatment evaluations in a laboratory system under simulated sunlight (UV-A = 140.2 ± 2.6 μW/cm2, UV-B = 6.40 ± 0.21 μW/cm2) (mean ± SE). Five concentrations of fluoranthene (0, 4.8, 9.7, 16.4, and 34.0 μg/L) and five concentrations of DHM (0, 0.5, 1.0, 2.5, and 5.0 mg C/L) were achieved. The presence of DHM reduced the acute photoinduced toxicity of fluoranthene. Regression analysis revealed that median lethal times (LT50) were directly related to DHM concentration and inversely related to fluoranthene water concentration. The presence of DHM also reduced fluoranthene bioaccumulation, and LT50 values were inversely related to fluoranthene body residues. These findings demonstrate that (1) the photoinduced toxicity of fluoranthene (like other polycyclic aromatic hydrocarbons) is dependent on body residue and (2) sitespecific environmental parameters that affect uptake and/or elimination can determine the rates of mortality due to photoinduced toxicity.