BIOSCREEN is used extensively for screening-level evaluation of the transport of dissolved contaminants in ground water. The code has an effective graphical user interface that makes it ideal for use in both professional practice and as a teaching aid. BIOSCREEN implements the approximate transport solution of Domenico (1987). This note describes an enhanced version of the program, BIOSCREEN-AT, which supplements the Domenico solution with an exact analytical solution. The exact analytical solution has been integrated seamlessly within the BIOSCREEN interface and provides a simple and direct way to calculate an exact solution to the transport equation and, if desired, to assess the significance of the errors introduced by the Domenico (1987) solution for site-specific applications. The modified version of BIOSCREEN is designated BIOSCREEN-AT and can be downloaded free of charge from http://www.sspa.com/./software/BIOSCREEN.htm.