MRI signals from two species such as fat and water are separated by repeatedly applying a steady state free precession (SSFP) sequence to an object with the phase of each RF excitation pulse in a sequence being increased by 2.pi.n/N radians on each repetition, where acquisition number n ranges from 1 to N. Alternatively, center frequency for each scan is incremented compared with the first scan center frequency. Images are reconstructed from the acquired signals and summed. Slowing varying phase due to sources other than chemical shift can be removed. Species signals are separated based on phase (sign) of the summed image signals.