On the basis of record linkage with the Social Security Institution's population register, 16 specimens from healthy subjects who subsequently developed systemic lupus erythematosus or mixed connective tissue disease could be traced from stored sera collected in connection with nationwide maternity welfare program in Finland. The sera were tested for antinuclear antibodies (ANA) using an immunofluorescence technique. Ten of the 16 specimens were positive. Eight of 11 cases were positive when the interval from taking the blood specimen to the onset of the first symptoms of disease was 2 years or less and 2 of 5 cases were positive when the interval was over 3 years. Eighteen of 21 sera with established disease and 5 of 85 control sera from the same serum collection were positive. Thus, ANA as detected by a sensitive technique frequently precede the onset of disease indicating that they are not a secondary manifestation of inflammation or tissue destruction.