1,6-Dinitropyrene (1,6-DNP) is a ubiquitous airborne pollutant found in diesel exhaust. In this study, mutagenesis was examined in the lungs of gpt-delta transgenic mice after intratracheal instillation of 0-0.1 mg 1,6-DNP. In addition, the 1,6-DNP-induced gpt mutation spectrum was compared with that of control mice. A single intratracheal injection of 0-0.05 mg 1,6-DNP resulted in significant dose-dependent increases in mutant frequency; the induced mutant frequency declined at the 0.1 mg dose. The average lung mutant frequencies at doses of 0.025, 0.05, and 0.1 mg 1,6-DNP were 2.9-, 4.1-, and 1.9-times higher than for control mice ((0.50 ± 0.16) × 10-5). The major mutations induced by 1,6-DNP included G:C → A:T transitions, G:C→T:A transversions, and 1-base deletions. Among the G:C→A:T transitions isolated from 1,6-DNP-treated mice, five (at nucleotide positions 64, 110, 115, 116, and 418) were observed in four or more animals. These positions therefore are potential hotspots for 1,6-DNP mutation. The predominant frameshift mutations following 1,6-DNP treatment included single base pair deletions at G:C (9/13 = 69%). The results of this study indicate that 1,6-DNP is mutagenic for the lungs of mice.