The freeze-drying technique can be of immense technological importance in the preparation of iron nanoparticles. Ultrafine (60-180 Angstrom) iron particles were produced with an excellent stability in air and remarkable magnetic properties by reduction at 200 degrees C of ultrafine haematite particles (30-50 Angstrom) which were prepared by decomposition of a freeze-dried iron nitrate precursor, The freeze-drying route appears to be a major step forward in the production and development of low cost particulate media for magnetic recording and ’throw-away’ iron catalysts.