Confidence intervals for effective concentrations (EC's) are commonly computed in dose response curve analyse. Profile intervals offer an alternative method for computing the confidence intervals in situations where delta method based confidence intervals produce intervals with values outside of a practical range. In this document, we describe the computation of profile intervals for EC's. We then introduce an R function, profile.ECx(), for computing these intervals from a dose response model fit by the drm() function in the drc package. Supplemental material includes three files of R code that define profile.ECx() and its helper functions and R code and data for the two examples.