Measurements of the microphonic potential from the lateral line sensory organs of killifish (Fundulusheteroclitus) are presented in this report. The potential consists of a dc shift and a dominant oscillatory component at twice the frequency of the stimulus, and it grows with the square of the stimulus at low amplitudes. An electrical circuit model of the microphonic is developed, assuming a simple quadratic nonlinearity in the electrical response of an individual hair cell as suggested by Flock. The model allows investigation of variable conductive or variable capacitive effects in microphonic generation, and the results obtained from the model are compared to the observed properties of the microphonic potentials. It is concluded that hair cell microphonics appear to be generated by a process involving current flow through a variable conductance, although capacitive effects of the hair cell are important in determining the waveform of the microphonic and its behavior as a function of frequency. A discrepancy between the observed low‐amplitude growth of the microphonic in killifish and the reported low‐amplitude growth of the microphonic in other acoustico‐lateralis preparations is also discussed.Subject Classification: [43]65.28, [43]65.20, [43]65.40.