This reminded of an article I once read, _The Blue People of Troublesome Creek_, by Cathy Trost, which appeared in the magazine _Science 82_, November, 1982, page 34. This article described the "blue Fugates", a family that lives in Kentucky, and many members of which are, well, blue. Really blue. So blue that doctors go nuts whenever one of them walks into a hospital or clinic for anything. A hematologist, Madison Cawein, eventually figured out that it was methemoglobinemia, a rare hereditary blood disorder that results in excess levels of methemoglobin in the blood. Methemoglobin (which is blue) is a non-funtional form of the normal hemoglobin which carries oxygen (and is red). In most people, normal hemoglobin is converted to methemoglobin at a very slow rate, and the enzyme diaphorase converts it back. The blue people, however, were lacking the converting enzyme. Cawein tried an injection of methylene blue, which acts as an electron donor (which is another way to convert the methemoglobin to hemoglobin), and people turned normal pink within a few minutes. Nowadays, they just take methylene blue pills. Cawein published his report in the _Archives of Internal Medicine_ in 1964. It turned out that the "disorder" (the people are otherwise extremely healthy) began in the 1920's when a French settler arrived (family history had it he was blue), and married a woman who must have been also carrying the recessive gene. Since the railway didn't come in until 1912, and local roads took another 30-40 years to lay down, the people were forced to intermarry, resulting in quite a few with both recessive alleles. Nowadays, as they marry out, the trait is disappearing, although some of the babies are blue for a few weeks after birth. It seems that newborns have lower amounts of diaphorase, and so they may appear blue for a short time, even if they only have one recessive allele. Yes, I suspect that these blue ferrets are due to something similar, but hormonally triggered. Probably they lose their diaphorase for a time after mating. Hormones are pretty powerful substances. MAnon [Posted in FML issue 1407]