While there are a multitude of video programs about Charles Darwin and Albert Einstein, there is a dearth of material on some of the other key personalities in the history of science, especially Gregor Mendel. I used to have a VHS copy of this program and it was excellent in showing Mendel's methods as well as the challenges he faced in doing his groundbreaking research on genetics. Mendel's story is truly a triumph the human spirit and intellect over the closed-mindedness of institutionalize religion and established science.
I have written to the people at PBS asking them to reissue it on DVD, but as yet with no positive result. If you teach biology, I assure you that you will want a copy of this. So please write to WGBH in Boston to request a DVD version.
UPDATE 2016 June 26: I am now retired, but see this program is now available on YouTube in 2 parts, so any teacher with high speed Internet access can view show it in class. As a substitute teacher, I have shown several NOVA and other science videos to classes via Internet streaming. However, usually having a DVD gives one somewhat more control over showing the program.