The broadening and shift of the optically thin Hg 577 and 491.6 nm lines emitted in high‐pressure mercury discharges operating at 50 Hz ac frequency are studied. An investigation is carried out in order to appreciate the influence of different factors on the broadening and shift of the local line profile. Comparison between computed and experimental apparent line shapes permits the determination of a set of broadening and shift parameters which leads to a satisfactory representation of the line shapes. Furthermore, applications to mercury discharge diagnosis are proposed.