Sensitized fluorescence in potassium induced by collisions with sodium atoms excited by a dye-laser radiation is investigated. In the experiment alkali dimer contribution to the process is negligible and self-trapping of the resonant radiation is avoided. The fluorescence intensity measurements yield the following cross-sections for collisional energy transfer from the2 P 1/2,3/2 resonance levels of sodium to the2 P 1/2,3/2 levels of potassium: $$\begin{gathered} Q(Na^2 P_{\tfrac{3}{2}} \to K^2 P_{\tfrac{3}{2}} ) = (0.9 \pm 0.2){\AA}^2 ,Q(Na^2 P_{\tfrac{3}{2}} \to K^2 P_{\tfrac{1}{2}} ) = (0.7 \pm 0.2){\AA}^2 , \hfill \\ Q(Na^2 P_{\tfrac{1}{2}} \to K^2 P_{\tfrac{3}{2}} ) = (1.2 \pm 0.3){\AA}^2 ,Q(Na^2 P_{\tfrac{1}{2}} \to K^2 P_{\tfrac{1}{2}} ) = (0.9 \pm 0.2){\AA}^2 . \hfill \\ \end{gathered} $$