Accurately measuring the growth of solid cultures is important for evaluating regrowth following low temperature storage, cell screening on selective media, or the suitability of different media formulations. However, current procedures are inadequate to provide precise, quantitative data non-invasively. This paper describes the development of an image analysis technique to provide quantitative growth data for callus cultures. Various properties obtained from image analysis, such as area, perimeter, diameter, and integrated density value, were correlated with the observed mass of plant callus. Based on this data, a predictive linear model was developed. The image analysis method was used to estimate cell mass as a function of various media components and growth conditions. This work demonstrates that image analysis is a flexible and useful tool for monitoring cultures.