The addition of D-3- and D-5-ethanol during Fischer-Tropsch synthesis with a promoted iron catalyst gives results that are consistent with ethanol initiating chain growth. However, there is considerable H/D exchange in the alcohol prior to initiating chain growth so that the D/molecule ratios in the alkane and alkene products are in the range 1.3-1.5. The nearly constant D/molecule ratio in the alkane and alkene products in the C-5-C-14 carbon number range is consistent with ethanol initiating chain growth. (c) 2010 Elsevier B.V. All rights reserved.