Abstract. A new sensor for evaluating fruit and vegetable firmness is presented while exemplifying application by reporting some results on measuring firmness of tomatoes. The firmness sensor comprises a small electrodynamic vibrator, which contacts the fruit and applies a series of minute input oscillations of a predetermined frequency and amplitude profile, optimized for each particular fruit type. These input oscil­lations are monitored by an acceleration transducer attached to the vibrator head. The output oscillations on the other side of the fruit, are measured by a similar transducer attached to the sensor finger, which gently contacts the fruit by a controlled force. The signals from the transducers are acquired by a microcomputer, which computes a firm­ness index, based on the difference between the output and input oscillation profiles. Firmer fruits transmit a larger portion of the input signal than softer fruits. For quality control and shelf-life prediction, the firmness of tomato samples may be measured manually, by a bench-top version of the apparatus. For research and for optimal harvest time determination, the portable hand-held version of the apparatus may be used for monitoring the firmness of tomatoes as they grow in the field or greenhouse.