We recently became aware of an unexpected hazard in our operations and would like to alert others to a situation that may be relatively common. Our investigation was prompted by a recent paper [E. C. Ashby et al., J. Am. Chem. Soc., 115, 1171 (1993)] that established conditions under which formaldehyde reacts with sodium hydroxide to give formic acid and hydrogen quantitatively. Typically, conditions also exist in which both this reaction and the classical Cannizzaro reaction proceed simultaneously. Ashby showed that reaction of 4 M NaOH with 15 mM formaldehyde led to production of hydrogen from 31% of the formaldehyde, the remainder going to normal Cannizzaro products. We wish to report that with only 0.5 M NaOH, 1-2% of the 20 mM formaldehyde present in our system is converted to hydrogen, which can create a significant safety hazard.