In vivo capillary examination was performed on 80 patients included in a prospective study of Raynaud phenomenon (RP): 40 RP only (RPO), 20 undifferentiated connective tissue disease (UCTD) and 20 systemic scleroderma (SD) of less than 5 years' duration. On initial examination, SD-pattern capillary abnormalities were found in 7/40 patients with RP alone, 18/20 with UCTD and 19/20 with SD. On follow-up a change of diagnosis into a definite connective tissue disease occurred in 4 patients with UCTD; one patient with RP alone died with symptoms of myositis and fulminant pulmonary vasculitis. All five showed SD-pattern capillary abnormalities of the "active" type on initial examination. A significant correlation between the "slow" capillary pattern and the presence of anticentromere antibodies was also observed. Only one patient of 25 RPO with normal capillaries available for follow-up showed any change in clinical status.