A follow-up study was done on 55 patients, all members of families with type I progressive familial heart block (PFHB) examined during 1977. Of the 55 patients 5 had died, 17 had normal ECGs while 7 with previously abnormal ECGs remained unchanged. All the others had progressed to a more severe form of heart block and 8 of them had received permanent pacemakers. These findings again emphasize the importance of regular ECG follow-up examinations of members of PFHB families.