The negative peak fluorescent detector previously described in this journal by Su and Winefordner1is used now to determine both fluorescent and non-fluorescent polynuclear aromatic hydrocarbons (PAH's). Here we report on limits of detecticn, linear dynamic ranges, calibration curve slopes and chromatographic retention times for several PAH's. We also report on the effect of solvent polarity upon the fluorescence signals when an HPLC separation is performed using a reversed phase packing and a polar solvent containing a fluorescent tag. The negative peak fluorescent detector is also shown to be useful in solvent programming studies.