Numerous peloids for balneotherapy are currently available but in terms of effects and efficacy therapeutic peat has been studied best. Recent studies revealed that both thermal and physical effects of therapeutic peat are comparable and synergistic. The thermal effects of all types of peat used are approximately the same but chemical effects differ. These results have to been taken into account in future peloid analyses and indications and contraindications of mud therapy have to be reviewed in this respect. Some hypothetical aspects of these chemical effects have to be investigated in future clinical studies but clinical experience with mud therapy allows preliminary conclusions to be drawn. This statement is especially supported by recent molecular investigations. Knowledge about the chemical effects is also necessary for planning, defining and designing clinical studies and patients groups. Exemplarily, the therapeutic use of peat in rheumatic diseases and for fertility treatment will be demonstrated.