The isolated stomach muscle strip preparation works well when given pure compounds which are stable and non-toxic. When complex test mixtures such as coffee are used, however, the results are more difficult to interpret. This is probably due to non-specific effects of such mixtures, e.g. induction of changes in organ bath pH, etc. In spite of the above remark, differences in the effects of decaffeinated and normal instant coffees were clearly seen. The so-called "wholesome" coffees gave results identical to those obtained with normal instant coffee. In general, coffee induced muscle contraction followed by relaxation. Choline (possibly together with potassium) would appear to be responsible for the contractions observed, and caffeine for the relaxation.