Transit spectroscopy is one of the best known methods to characterise the exoplanets atmosphere. Ground-based detections of atomic sodium in the atmospheres of well-known planets, e.g. HD189733b (Redfield et al. 2008 ; Jensen et al. 2011 ) and HD 209458b (Snellen et al. 2008), were enabled by the use of high-resolution spectrographs (R~50 000). Here, we present our results about the sodium search in the atmospheres of HD 189733b and WASP-69b by using HARPS and HARPS-North (R~115 000) observations, respectively.