The Feldt-Gilmer congeneric reliability coefficients make it possible to estimate the reliability of a test composed of parts of unequal, unknown length. The approximate standard errors of the Feldt-Gilmer coefficients are derived via a method using the multivariate Taylor's expansion. Monte Carlo simulation is employed to corroborate the theoretical approximations for eight hypothetical tests. The Feldt-Gilmer coefficients are shown to be appropriate with both congeneric and tau-equivalent parts. Their superiority over the special case of Kristof's coefficient increases with the number of parts. Their standard errors also compare favorably to that of Cronbach's alpha coefficient when applied to tests with tau-equivalent parts. Tables illustrate the charts. (Author/CM)