Noise loading has a considerable effect on the working conditions of telephone operators. This study comprises noise field and laboratory measurements and field investigation of workers at three departments of the Telephone and Telegraph Communication Services in Sofia. Noise measurements revealed a background noise in the range of 57.4-70.6 dB A in the International Department, 70.6-71.7 dB A in the Intercity Department and 68.7-70.1 dB A in the Information Department and highest intensities of 63.5, 62.1 and 58.2 dB for frequencies of 0.5, 1 and 2 kHz. The registered noise (Leq) from the inner telephone receiver-microphone (type Star-set) was in the range of 78.4-86.6 dB A. Peaks of 90-96 dB A were registered during different working operations ("dialing", "speaking", "fax", "occupied") with duration less than 5s and stochastic appearance during the 15 min measuring periods. A total of 260 female telephone operators (mean age 36.7 +/- 8.22 years and mean length of employment 12.7 +/- 7.12 years) with similar job activities at the three departments were investigated. No marked decreased hearing sensitivity for 0.5, 1, 2, 4, 6 and 8 kHz was observed. A high percentage of the examinees gave positive answers in different questionnaires regarding subjective symptoms (psychological, neurovegetative, neurological), mental health, depression and anxiety. An elevated urine excretion of catecholamines (11-OCS, adrenalin and noradrenalin) was found during the morning and afternoon working shifts. The intensity of the noise and its annoying effect were subjectively estimated as "high" and "very high" by most of the examined telephone operators. In a large percentage of operators in the Intercity Department, the changes of the audiometric, psychological and biochemical examinations were more pronounced. The obtained results indicate that redesign of the work place should be undertaken in order to prevent health effects on the telephone operators.