Lognormal distributions have applications in health sciences, occupational exposures, environmental monitoring and several other fields. In this article we compare power functions of four testing procedures based on Student-t, Edgeworth expansion, generalized p-value, and permutation test for testing the mean of a lognormal distribution. We recommend the generalized p-value and permutation test procedures for testing the mean of the distribution. Using these procedures we also determine the required sample size for obtaining a pre-specified power. The results are illustrated with an example from an environmental monitoring field.