Abstract An intervention study aimed at reducing the occurrence of low back disorders was carried out among 88 planners and 125 sheet metal workers in a ventilation equipment producing plant in 1986–1990. Attempts were made to improve working conditions, knowledge about how to use the back at work and fitness of the back tissues using a participatory approach. Base-line values were determined for lumbar function, load on lumbar spine at work, occurrence of low back pain and take-up of sick-leave benefits. After the intervention, the sheet metal workers considered the load on the back smaller than before; this was verified by biomechanical evaluation of the work tasks. More workers reported adhering to ergonomic work principles and using technical equipment for lifting. Comparing the period 1985–1989 to 1990–1991 the occurrence of sick-leaves of up to six months due to low back disorders fell from 3.1 to 1.9 days/person-year.