In this paper, the transient and steady-state performance of a liquid to air membrane energy exchanger (LAMEE) is investigated experimentally. The transient sensible, latent and total effectiveness are each presented for particular air and desiccant mass flow rate for both summer and winter supply air test conditions. After a step change in inlet conditions the effectiveness increases with time. Also, the transient effectiveness is assessed for various air and desiccant mass flow rates under summer test conditions and the LAMEE's time constant is investigated as an important variable that depends primarily on the thermal capacity of the exchanger and liquid content. The calculated effectiveness shows considerable dependency on the air and desiccant mass flow rate. Finally, steady-state results reveal that as the desiccant mass flow rate increases or air mass flow rate decreases, the effectiveness increases. (C) 2012 Elsevier Ltd. All rights reserved.