Andersson AM, Carlsen E, Petersen JH and Skakkebaek NE, 2003, J Clin Endocrinol Metab, 88, 932-937 , Variation in levels of serum Inhibin B, testosterone, estradiol, luteinizing hormone, follicle-stimulating hormone and sex hormone binding globulin in monthly samples from healthy men during a 17-month period: possible effects of seasons