The angle dependence of the magnetoresistance (MR) of (ET)2(SCN)4 (M=K,NH4) has been measured in steady magnetic fields up to 50 T. In (ET)2KHg(SCN)4 We observe two SdH frequencies in the MR below the resistive ''kink'' feature at 22 T, and different values of g*m* above and below the ''kink''; we propose that these effects result from antiferromagnetic ordering between the conducting planes. In (ET)2NH4Hg(SCN)4 we have found that both the frequency of the Shubnikov-de Haas (SdH) oscillations and the effective mass of the carriers vary to a high degree of accuracy as 1/cos(theta) (theta is the angle between the field and the normal to the conducting layers) as expected for a quasi two-dimensional system, and in contrast to a previous study by others. Finally we comment on the validity of the ''Harmonic Ratio'' method for measuring effective masses.
