Formalin and alcohol are routinely used as preservatives for biological specimens in museum collections and biological and medical laboratories. In some cases the identity of the preservative fluid that a specimen is contained in is not known, but must be discovered before the specimens can be transferred to an appropriate permanent preservative. The traditional method for distinguishing between formalin and alcohol solutions has been to sniff the preservative. Because formaldehyde is irritating, toxic, and probably carcinogenic, a safer test for distinguishing formalin from alcohol was developed. The test employs strips of filter paper containing an acid/base indicator and a mixture of sodium sulfite and sodium metabisulfite. These test strips respond rapidly to aqueous formalin solutions containing more than about 1.5% formalin by changing color from yellow to red. The test strips are inexpensive and simple to make and to use. -- AATA