An investigation was made to search for the recoilfree gamma transition of Fe⁵⁷ in blood and in blood components. Using a single crystal of hemin, a directionally dependent Mossbauer effect can be expected. The recoil energy for a free iron atom, a rigid hemin molecule, a hemoglobin molecule, and one red cell emitting or absorbing a 14.4 kev gamma ray is given according to the equation ER (atom = E/2mc². A source of Co⁵⁷ diffused in Cu was used. The absorber consisted of 135 mg hemin/cm² held between thin aluminum foils mounted in a holder and connected to a liquid nitrogen cryostat. It was found that the hemin curve shifted toward the center (zero velocity) by a very small amount (about 0.01 cm/sec) and the line width was nearly twice as large. The isomer shift (or chemical shift), which is a measure of the electron density at the nucleus, was indicative of the chemical binding of the iron atom. (P.C.H.)