Since 1974, life tests with heat pipes for space applications have been carried out at IKE under contract to the European Space Agency (ESA)-Presently, five stainless steel/ammonia artery heat pipes and six axially grooved aluminium/ammonia heat pipes are being tested. Each heat pipe undergoes two different test procedures, viz. life tests and maximum performance tests.With the artery heat pipes, essentially no degradation of maximum performance and isothermality could be observed over the whole testing period. The aluminium axially grooved heat pipes show temperature differences increasing slightly with life time. Several axially grooved heat pipes show temperature differences increasing slightly with life time.exhibit a sharp temperature drop at the end of the condenser section.