The Biostack experiments I and II were flown on board the Apollo 16 and 17 command modules in order to obtain information on the biological damage produced by the bombardment of heavy high-energy (HZE) particles of cosmic radiation during spaceflight. Such data are required for estimating radiation hazards in manned spaceflight. Seven biological systems in resting state (Bacillus subtilis spores, Colpoda cucullus cysts, Arabidopsis thaliana seeds, and eggs of Artemia salina, Tribolium castaneum and of Carausius morosus) were accommodated in the two Biostacks. By using a special sandwich construction of visual track detectors and layers of biological objects, identification of each hit biological object was achieved and the possible biological damage correlated with the physical features of the responsible HZE-particle. In the different systems the degree of damage depended on whether the hit cell was replaceable or not. A high sensitivity to HZE-particle bombardment was observed on Artemia salina eggs; 90% of the embryos, which were induced to develop from hit eggs, died at different developmental stages. Malformations of the abdomen or the extremities of the nauplius were frequently induced. In contrast, the growth of hit Vicia faba radiculae and the germination of hit Arabidopsis thaliana seeds and hit Bacillus subtilis spores were not influenced remarkably. But there was an increase in multicaulous plants and a reduction in the outgrowth of the bacterial spores. In addition, information was obtained on the fluence of the HZE-particles, on their spectrum of charge and energy loss, and on the absorption by the Apollo spacecraft and the Biostack material itself. This will help to improve knowledge concerning radiation conditions inside of spacecrafts, necessary to secure a maximum possible protection to the astronauts.