The functional relationship between intensity(I) of an emitted line and concentration ( C ) of emitting atoms serves as the physical basis for quantitative spe-ctrochemical analysis. The presence of self-absorption in spectral lines of most laboratory light sources, however, makes the dependence of I on C complicated.A study of variation of slope ( b )of the calibration curve (Si 2516-Fe 2518) with concentration of silicon in cast iron samples by the "transfer method" of spectral analysis was carried out under the condition that within the range of Si content studied, Si 2519 was free from self-absorption and Si 2516, the most intense component of the multiplet was showing self-absorption. A straight line has been obtained by plotting 6 versus log I2519 which was used as a measure of log C. From the slope ( k ) of this straight line, following relationships were derived: b=klogC+β+1,(1) and logI=k/2(logC)2+(β+1)logC+α, (2) where β and α are experimental constants. In the case of Si 2616, the value of k has been found to be about-(1/2) The change of spectral intensity with concentrationin the presence of self-absorption expressed by equation ( 2 ) was found to be in agreement with laboratory observations in general.