The frequency of micronuclei (MN) in cells of the nasal mucosa, oral mucosa and in lym-phocytes was evaluated for 25 students in anatomy classes exposed to formaldehyde (FA) overan 8-week period. Each student served as his or her own control. The time-weighted averageconcentration (TWA) of fOrmaldehyde in anatomical laboratories and in students’ dormitorieswas 0. 508 ± 0. 299 mg/m3 and 0. 012 ± 0. 0025mg/m3, respectively. A higher frequency ofmicronuclei was observed in nasal and oral exfoliative cells after formaldehyde exposure (3. 85± 1. 48 vs 1 .20± 0. 676 and 0. 857 ± 0. 558 vs 0. 568 ± 0. 317, paired-t test: P< 0. 001and P < 0. 01, respectively). No significant increase in the frequency of lymphocyte micronu-clei was found after formaldehyde exposure (P >0. 05 ). The present study shows that nasalmucosa cel1s exposed through respiration are the chief target of FA-induced genotoxic effects The frequency of micronuclei (MN) in cells of the nasal mucosa, oral mucosa and in lym-phocytes was evaluated for 25 students in anatomy classes exposed to formaldehyde (FA) overan 8-week period. Each student served as his or her own control . The time-weighted average concentration (TWA) of fOrmaldehyde in anatomical laboratories and in students’ dormitories was 0.508 ± 0. 299 mg / m3 and 0. 012 ± 0. 0025 mg / m3, respectively. A higher frequency of micronuclei was observed in nasal and oral exfoliative cells after formaldehyde exposure (3.85 ± 1.48 vs 1.20 ± 0.67 and 0.857 ± 0.558 vs 0.568 ± 0.317, paired-t test: P <0.001 and P <0.01, respectively). No significant increase in the frequency of lymphocyte micronu-clei was found after formaldehyde exposure (P> 0.05). The present study shows that nasal mucosa cel1s exposed through respiration are the chief target of FA- induced genotoxic effects