Abstract: The invention contemplates, for use with an inverted microscope, a specimen holder having a relatively wide range of capability for replaceably accepting and holding any one of a variety of sizes and shapes of specimens. Aside from the specific capability of accepting standard-size microscope-specimen slides, the holder can equally well and positively mount circular specimen supports of various diameters, such as Petri dishes or Erlenmeyer flasks. In one disclosed form, the release and clamp operation of the holder is a simple one-handed operation, leaving the other hand of the operator free for other purposes.