To investigate the question as to the possibility of damage being done to the human organism by diagnostic ultrasound--with particular emphasis on the aspect of a possible cumulative effect--we investigated 20 people employed by two companies manufacturing ultrasonic equipment, who had been exposed for between 13.5 and 1,000 hours (average 152 hours) over periods varying between 0.75 and 11 years (average 4.2 years). During the examination, which included a thorough clinical work-up, haematological, laboratory and ultrasonographic investigations, particular attention was paid to the liver and blood, since the liver is usually chosen for demonstration and test purposes, and the blood is always exposed to the effects of ultrasound. We found no evidence of any harmful effect of ultrasound on the human organism, nor were there any tendencies correlated with the period of exposure to be found. A newly detected diabetes mellitus was interpreted as an incidental finding.