By means of continuous recording of the positions of the trunk and head, an investigation was carried out to examine the effect of the Erasmus office-desk - a desk with a 10° inclination - on sitting posture whilst reading and writing, sitting in an adjustable chair at an adjustable table. The posture assumed by a person who is doing mixed reading and writing work at a table with the Erasmus office-desk is more upright than the posture of the same person doing the same work without the desk. This applies for both the head and the trunk. The average position of the trunk was changed from 26·0° to 18·2° when working with the desk placed on the table. The moment of force caused by gravity is proportional to the sine of the angle. Therefore the change of angle results in a decrease of the average moment of force on the back at L5-S1 of 29%. The largest individual decrease found was 86%. The average change of the position of the head was changed from 38·5° to 29·6°, resulting in an average decrease of the moment of force, on C7-T1, of 21%. The largest individual decrease was 51%. Lateroflexion of the back was less often assumed when the subjects were using the desk. The posture assumed by the subjects when they were doing writing work only was generally more upright when working at a desk with a 10° inclination than when working at a flat desk. Marked differences were found between the postures of the subjects. The change of posture while using the desk also showed marked differences for each subject individually.