When a family of genes from closely related organisms is known, there is a certain change to extract the corresponding gene from the genome of another related organism. This can be done by polymerase chain reaction, provided that a pair of suitable primers can be designed. In contrast to primer design for a single, known target sequence, systematic primer design for an unknown target given a group of homologues can by no means be done manually. GeneFisher is a software tool which automates this task, and takes special care to make the impact of the manifold design parameters transparent to the user.