The frequency of HLA-Dw1-8 and DH was determined in 389 unrelated healthy Danes and in 257 kidney patients. All individuals were HLA-A, B, C typed, 168 of the normal individuals and all kidney patients were typed for HLA-DR. The frequency of Dw1-8 in the normal material and kidney patient material was quite similar except for Dw6, which showed an increased frequency among the kidney patients, but as the patients are not prospectively ascertained, the significance of this finding is unclear. The frequency of the blank allele is 0.19 which is comparable to other Scandinavian materials but much lower than that seen in the joint report of the 8th International Histocompatibility Workshop. The D frequencies correlate quite well with the HLA-DR frequencies, the biggest discrepancy between D and DR exists for D/DR4, where DR4 is much "broader". The DR4 positives can be divided into the Dw4 positives, strongly associated with B15 and the Dw4 negatives, not associated with B15 but with B40. Primed lymphocyte typing in some cases followed HLA-DR, in other cases HLA-D assignment. For HLA-D/DR2 the DR assignment also seemed to be broader, the DR2 positive, Dw2 negative group not being associated with B7, but possibly with B5. In the assignment of HLA-D determinants, "false negatives" have caused problems in many materials, but the inclusion of a number of known control responders in our experiments has made it possible to increase the accuracy of assignment by adjusting the cut-off level for typing responses according to the typings of the controls.