DNA adducts represent the putative initiating event in the chemical carcinogenesis process. (32)P-Postlabeling is one of several assays which have been developed for the sensitive detection of DNA adducts. An integral part of the (32)P-postlabeling assay is the separation of adducted nucleotides by multidirectional, multisolvent, anion-exchange polyethyleneimine-cellulose thin-layer chromatography. In the study the use of a dilute ammonium hydroxide solvent for D4 chromatography is introduced and compared to other standard solvents such as lithium chloride-Tris/HCl-urea, sodium phosphate--Tris/HCl-urea, and isopropanol-4 M ammonium hydroxide for adduct separation, resolution, recovery, retention of background noise, and chromatography development time. 0.2 M ammonium hydroxide worked well for the recovery, separation, and resolution of a wide array of adducts derived from highly lipophilic polycyclic aromatic hydrocarbons and aromatic amines. In addition, this solvent required much less time (< 1/4) as compared to the other solvents and more importantly allowed the separation of adducts which otherwise comigrated and were not visible when using the other three D4 solvents. Background radioactivity per sq cm of the thin layers was also reduced two- to three-fold with the ammonia solvent versus the urea-based solvents. Thus, the use of this dilute ammonia system provides powerful resolution in a time-efficient manner.