Objective: Little attention has been paid to the effects of electromagnetic field (EMF) of mobile phones on hearing. The aim of this study is to investigate the effects of chronic exposure to EMF emitting from mobile phones on the inner ear of adult and developing rats using distortion product otoacoustic emissions (DPOAEs). Methods: EMF of mobile phones exposure was scheduled according to a sham-exposure controlled experimental design. Every day seven of 14 adult and four newborn rats were exposed to 1-h mobile phone EMF for 30 days, while the other seven adult rats were assigned to control group. DPOAEs were measured in both groups before and after the chronic exposure to EMF. The newborn rats were tested following similar exposure beginning on the 2nd day after birth. Results: No measurable EMF associated changes in DPOAEs either in adult or developing rat inner ears were determined (P > 0.05). Conclusion: It was concluded that chronic exposure of EMF, as long as 30 days 1 h per day, emitting from a mobile phone did not cause any hearing deterioration in adult and developing rats, at least at outer and middle ear and cochlear levels. (C) 2003 Elsevier Science Ireland Ltd. All rights reserved.