Cortical thickness of the second metacarpal bone and lumbar spine fractures were determined radiographically in twenty-one Caucasian corticosteroid-dependent asthmatics (mean age, 61-2 years; range 47-73 years). The mean number of prednisone years per patient of continuous corticosteroid treatment averages 9.7 (range 5.0-21.5 years), and the mean accumulated dose of prednisone was 46.7 g (range 10.7-160 g). Thirteen of twenty-one (61.9%) patients had cortical thickness between 1 and 2 standard deviations (s.d.) below the age- and sex-specific mean for normals, but only four (19%) patients fell below 2 s.d. Although the study indicated decreased cortical thickness in the prednisone-treated group, in only one (4.8%) patient were vertebral fractures present, an incidence not unexpected in this age group. In serious chronic asthma, concern for bone structure should not prohibit the cautious use of appropriate corticosteroid regimens at the lowest possible maintenance dose.