Abstract: A spectrophotometer which accommodates a self-contained sample module. Sample modules are interchangeable and can be readily inserted into, or removed from, the spectrophotometer without tools. Guides in the spectrophotometer assure that the modules are properly aligned when inserted. The module houses the sample(s) to be tested. Sample cell holders may be removed from the module and replaced with other cell holders. When the module is inserted into the spectrophotometer, optical alignment, mechanical alignment, proper electrical connection and software interface are all achieved in one common installation procedure for all sample modules.