The uniaxial anisotropy field Haof nominally single acicular particles was measured by three different methods, and the coercivity was also found. A very dilute suspension was made in a viscous liquid, and a particle observed with the microscope. Various types of magnetic field were then applied, and the particle's change in orientation enabled and/or Hrto be determined. One method gave anomalously low values for Ha, but it was possible to reconcile the results. The larger values lay in a range consistent with the chain-of-spheres and prolate ellipsoid models. There was a linear relationship between Haand Hr(or Hc). The results suggested new reversal mechanisms.