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Simultaneous application of two methods for the detection of anti-native DNA antibodies (indirect immunofluorescence on DNA fibres and Farr's radioimmunological method with native DNA labelled C14) to 53 serum samples from 32 patients suffering from systemic lupus erythematosus (SLE) indicated a certain number of discordances between the results obtained. Correlations between clinical and laboratory findings were found, such that certains types of anti-native DNA antibodies (n) may be specific to certain clinical manifestations of SLE: a good correlation was seen between She fixation of anti-C14 nDNA and the titre of IF anti-nDNA in the group of SLE with renal involvement, but was not found in the group of SLE with central nervous system involvement. There was no parallel between the course of renal involvement and anti-nDNA antibody titres, without treatment being directly responsible. The significance of the presence or absence of anti-DNA antibodies with the two methods of detection used is not of any single significance. Several types of anti-nDNA antibodies are present in a given specimen of lupus serum. Certain anti-nDNA antibodies are not detected or are at the limit of a positive result in the presence of neurological manifestations. From a practical standpoint, the use of several laboratory tests is desirable for the possible investigation of SLE.

Three methods of determination of anti-DNA antibodies were compared. The indirect immunofluorescence method after exposure to animal DNA (IF) and Farr's radio-immunological method with bacterial DNA labelled with C14, gave highly similar results, although there were some cases in which Farr's method gave a negative and the IF method a positive result. In part, this discordance appears to be accounted for by the variable affinity of the anti-DNA antibodies for DNA. The counter-immuno-electrophoresis method (CIEP) on the other hand, gave very different results: positive reactions in a large proportion of normal sera and a considerable proportion of false-positive and false-negative results in disseminated lupus erythematosus. It is concluded that until the CIEP method is made more reliable by technical refinement, determination of anti-DNA antibodies may be carried out by either the IF or the radio-immunological method, but a double-check, by application of the two methods at the same time, is highly advisable.