In the general population there is an increasing tendency to attribute health damage to exposure to hazardous substances in the environment. With the increasing demand for consultation and care there is at present a growing need for doctors specialised in environmental medicine. In the Federal Republic of Germany environmental medicine is represented in particular by environmental hygiene and clinical environmental medicine. Clinical environmental medicine can be characterised as being halfway between care and clinical diagnosis with emphasis on secondary prevention (early recognition of any disturbance of health). The discipline is geared to the individual and this means that the diagnostic strategy and risk evaluation must be considered individually for every case. In addition to scientific facts of environmental toxicology and epidemiology, fundamental medical and pathophysiological knowledge must also come into play. A scientifically founded medical appraisal clarifying possible negative effects on health due to hazardous substances in the environment is presented, based on long-standing experience gathered during consultation work on environmental medical problems at the Institute for Occupational, Social and Environmental Medicine of the University of Erlangen-Nuremberg. Focus is mainly on the effects of chemicals. To evaluate the individual risk, an analytical procedure of many steps is required which includes in particular the collection of anamnestic data specific to the problem, objectifying and quantifying of exposure to hazardous substances and/or specific biological effect reactions, limitation of competing influences and an overall medical assessment of environmental toxicity.