Na vapour was excited by the sodium D2 line.The 3P→3S
5S→3P
4D→3Pfluoresence intensities were detected.Cross section (2.4×10-15cm2) for collision-al excitation energy transfer in Na(3p)+Na(3p)→Na(4D)+Na(3S)was mea-sured.Our experimental result coinsides with data reported in the references.