Radiogrammetry remains a convenient method of bone mass measurement. It is the only objective means of quantifying metacarpal osteoporosis (OP) in rheumatoid arthritis (RA). An automated technique using a digitizer (interfaced with an IBM PC) for measurement of combined cortical width (CCW) at the mid-shaft of six metacarpals was evaluated in three groups of individuals under 50 years of age (98 normal controls, 96 RA, 63 SLE). Intra-observer, inter-observer, and inter-institution reproducibility was assessed with a 'phantom' embedded in a rectangular mould of wax. Intra-patient variation was also assessed in RA patients seen on two occasions less than a month apart. Two hundred and fifty-seven subjects were studied. The method was found to be reproducible for a single observer, among five different observers and in two separate institutions. The RA subjects seen on two occasions showed no significant differences in CCW. The technique showed significant differences of CCW in the three groups of premenopausal subjects (controls; RA; SLE) studied (p less than 0.001). The six metacarpal bone mass was calculated in less than 5 min. The technique of digitized radiogrammetry is an improvement on the Vernier caliper technique. The method is useful for epidemiological cross-sectional studies and for evaluation of long-term radiological changes in RA.