Experimental development of in-pile equipment over the last ten years has resulted in the design of unique systems involving a variety of experiments. The experiments range from simple corrosion and fuel irradiation tests to complex irradiation environment studies and fast reactor fuel failure tests The paper summarizes the type of facilities designed at the Argonne National Laboratory for these experiments and describes the purpose for which the design was intended. in addition, typical values for test parameters are included to acquaint the reader with the conditions encountered during a test. The intent of the paper is to demonstrate the span of engineering experiments possible in reactors. Consequently, the results of the tests are not described or discussed since these results have been published m other papers. Instead, attention is directed toward the nature of equip-ment which has been brought into existence.