Sphalerite in the Late Proterozoic Meixian massive sulfide deposit, Youxi county, Fujian province, is heavily infected with the chalcopyrite disease. As revealed by etching in 50% HNO3, chalcopyrite viruses occur mostly as blebs, rods and worms several microns in size inside sphalerite grains and along cleavages and twin faces of sphalerite. Chalcopyrite viruses occupy more than 5% in volume of the sphalerite. Such a high density of viruses and hence the high con-tent of copper in sphalerite can not be explained in terms of chalcopyrite exsolution. Chalcopyrite viruses are seen, in some cases, connected with chalcopyrite veins and patches cutting and replac-ing diseased sphalerite in the same samples, inplying that the viruses should have been produced by replacement of the sphalerite. Electron microprobe analyses on two profiles across chalcopyrite blebs in sphalerite show that there is no Fe content decrease in the sphalerite in the close vicinity of the viruses, indicating that the fluid for the replacement has introduced Fe as well as Cu to the sphalerite.