The need for a relatively high-speed analogue multiplier is discussed and the types of multiplier likely to meet this need at reasonable cost are investigated. It is concluded that the modulated square-wave type of multiplier using transistor modulators will be most suitable.The extension of the scope of the multiplier to operate with inputs of either sign is discussed. The causes of the various errors in the multiplier are examined and an overall accuracy of within ±2% is quoted. An explanation of the method used to ensure a good frequency response is given, and the transfer function of various parts of the circuit analysed. The experimental results are quoted as being similar in amplitude to a transfer of 1/(1 + 5 × 10−4jω), although the phase shift is considerably better than this.A number of circuits used to protect the transistors against damaging conditions are discussed. Special attention is given to a separate transistor circuit which disconnects all the power supplies in the event of an irregularity in any one of them.