Has science become so politicized that regulation is dictated by desired political outcomes and not legally mandated considerations of public health and safety? Changes in regulation between administrations is not unusual, but ordinarily these changes are differences in degree of regulation based on scientific variances within a generally accepted range of scientific conclusions. Recently, however, regulatory reversals have been just that---complete reversals based on scientific determinations that flatly contradict conclusions reached only a few years,or even months, earlier within the same agency. For example, one federal judge frustrated with the yo-yoing federal policy on snowmobiles in Yellowstone National Park, chided the agency for claiming a change in scientific basis without justification. Environmental advocates are challenging EPA's relaxed position on controlling mercury air emissions for totally ignoring a Harvard study on point released just weeks after EPA's determination and provided in draft form to the agency precisely for its consideration. When is science "junk science" and how and when can courts reject science offered by agencies to justify their decisons?