Natural wastewater treatment has become increasingly important to safeguard public health communities from wastewater associated infectious diseases. Constructed wetlands have been promoted in recent literature for use in rural communities in developed as well as in developing countries being an appropriate technology to be handled with low operational maintenance costs. Constructed wetlands have been investigated within a joint project, supported by BMBF (Project No O2WA0107 and No 02WA0108) concerning the sanitation effect on wastewater effluents. This dissertation will focus on the detection and the removal of cysts of Cryptosporidium parvum and Giarda lamblia, those being worldwide the most frequently identified pathogenic protozoan parasites with increasing medical and economical consequences. Two plants, one installed in 2000 as a pilot plant at Langenreichenbach near Leipzig (Saxonia, Germany), the other one routinely run since 1993 in a training center at the town of Belzig (Brandenburg, Germany) were tested overall for three years. Detection methods from US EPA (ICR Protozoan Method for Detecting Giardia Cysts and Cryptosporidium Oocysts in Water by a Fluorescent Antibody Procedure (EPA/814-B-95-003; US EPA 1995)) were employed in order to assess. protozoal and bacterial reduction in the wastewater passing different combinations of filter beds and fillings. Removal of cysts of Cryptosporidium and Giardia spp. turned out to be a 2 log reduction in all plants. Highest reduction rates could be shown for Giardia spp. whereas Cryptosporidium oocysts only were detected sporadically in the influent of both plants. The most effective structural element was a two-stage combination of filter beds leading to the highest removal efficacy both for the protozoan and the bacterial indicator organisms. Also, small sand particles (> 2 mm size) in the filter bed proved to be most effective filter material; the planted weed, however, turned out to be of minor importance for the filtering activity. Wastewater effluents from those types of plants we tested may be used as irrigation water according to the WHO guidelines; however in case of a high load of protozoan parasites these requirements might not be met. Since literature shows no direct correlation of protozoan burden linked to other indicator organisms like bacteria and viruses, any use of the gained water must be connected to close controls of the water quality.