Here we present a novel method termed full-length normalization subtractive hybridization (FNSH) for efficiently generating subtracted cDNA libraries with a high degree of productivity. This method has the ability to isolate full-length differentially expressed genes from target samples. Normalization and subtraction of FNSH are performed simultaneously with efficiency equal to or even higher than that of suppression subtractive hybridization. Using FNSH, we have isolated at least 40 unique cDNAs that are expressed in terminal ampullae but not in the ovaries of the prawn Macrobrachium rosenbergii from 120 randomly picked subtracted clones. Sequence analysis shows that 37 of the 40 cDNAs are full length.