The use of sodium hyaluronate in 383 cases of Cataract extraction with primary lens implantation has been to be effective, non-toxic and safe. Chief uses are to protect the corneal endothelium during nucleus extraction and to maintain the anterior chamber depth during lens implantation and during iris suturing. It is important not to use excessive amounts and to dilute with miochol or salt solution during wound closure. Using these techniques sodium hyaluronate was found to be free from side effects and when timolol maleate was used b.d. from the close of surgery the incidence of postoperative ocular hypertension was found to be no different from that in a control group. Endothelial cell studies showed a cell loss of 13 per cent to be within the range previously established for intracapsular cataract surgery without lens implantation, and support a widening conviction that lens implantation may now be regarded as a safe procedure.