Whatever the purpose of test adaptation, questions arise concerning the validity of inferences from such adapted tests. This paper considers several advantages and disadvantages of adapting tests from one language and culture to another. The paper also reviews several sources of error or invalidity associated with adapting tests and suggests ways to reduce those errors. It also considers test adaptation advances in a rapidly emerging area of social research, quality of life measures. The term "test adaptation" is preferred to test "translation" because adaptation is a broader term that better reflects what should happen in preparing a test that is constructed in one language and culture for use in another language and culture. Adapting a test may be cheaper than developing a new test, and it may allow better cross-cultural comparisons, provide a greater sense of security, and enhance fairness. Sometimes, test adaptation is not the answer, and when it is a good approach care must be taken to ensure validity. Sources of error that arise in test adaptation can be organized into three broad categories: (1) cultural and language differences; (2) technical methods; and (3) interpretation of results. Each of these must be considered in the adaptation process. The use of quality of life (QOL) tests by medical and public health researchers is a growing area that requires more than mere translation of the test. Suggestions are made to ensure that the adaptation of QOL tests receives the rigorous judgmental analysis it deserves. (Contains 28 references.) (SLD)