The absorption coefficient for excitons is calculated in the effective-mass approximation. The coefficient is shown to be decreased over what one would expect for a collection of free atoms by the factor ${\ensuremath{\epsilon}}^{\ensuremath{-}1}{(\frac{{a}_{0}}{{a}_{B}})}^{3}$, where $\ensuremath{\epsilon}$ is the dielectric constant and $\frac{{a}_{0}}{{a}_{B}}$ is the ratio of the lattice constant to the exciton radius. This result seems not inconsistent with the identification of the observed absorption lines in ${\mathrm{Cu}}_{2}$O, CdS, Hg${\mathrm{I}}_{2}$, Pb${\mathrm{I}}_{2}$, and Cd${\mathrm{I}}_{2}$ as exciton lines.