Modern methods of treatment have led to major improvement in the survival rate of children with Wilms' tumor. The combination of surgery, radiation therapy and chemotherapy cures up to 80 percent of patients. It is recognized however, that all treatment forms have their risks and complications. The National Wilms' Tumor Study (NWTS) was initiated in 1969 in order to refine methods of therapy and understand the disease better. Groups of investigators in several institutions with a common interest in the Wilms' tumor problem agreed to combine their efforts in a single investigation. Three of the national cooperative study groups have joined in this endeavor. The objectives of the Study are now approaching realization. The therapeutic questions were concerned with the role of radiation therapy and of single agent versus combined chemotherapy. Additional objectives included a better understanding of the neoplasm by grouping patients according to specific patterns of tumor involvement and by histologic type, and correlating these patterns and types with eventual response to treatment and survival. Significant differences in the results achieved among the various study arms are appearing at an earlier date than anticipated. This makes necessary an expanded effort in the Data and Statistical Center. Additional personnel are required in order to accelerate the analysis of the unique body of information accumulated in the NWTS so that this information can be used with maximum efficiency and dispatch, and the information be made available to the medical world at an early date. Supplemental funds are required for those purposes.