The present paper briefly reviews the different direct liquid-feed fuel cells that have been regarded through the open literature. It especially focuses on thermodynamic-energetic data and toxicological-ecological hazards of the chemicals used as liquid fuels. The analysis of those two databases shows that borohydride, ethanol and 2-propanol would be the most adequate liquid fuels for the polymer electrolyte membrane fuel cell-type systems, even if they are inferior to hydrogen. All the fuels and also all the by-products stem from their decomposition are more or less harmful towards health and environment. More particularly, hydrazine should be avoided because it and its by-product are very dangerous. It is to note that the present paper does not intend to review and to compare the performances of those fuel cells because of great differences in the efforts devoted to each of them. (c) 2007 Elsevier B.V. All rights reserved.