SUMMARY: Specific high titre antisera were raised in three out of four rabbits injected with 100/μg each of a highly purified FSH preparation by the multi-site intradermal immunization technique. High titre antisera were also raised to LH, TSH, HCG, and the α sub-unit of HCG. Immunization with human GH- and LH-releasing hormone did not result in such high titre antisera. The implications of the results are discussed.