ACDP is a Java application for processing protein circular dichroism (CD) spectra either individually or within a series. Data processing includes spectrum subtraction (`baseline correction'), conversion of the raw CD into units of mean residue ellipticity, wavelength monitoring and graphical inspection. Three different algorithms for secondary structure deconvolution have been implemented, and spectra can be analysed without the need for data reformatting, using a neural network approach, variable selection or linear combination of prototype spectra. The application is written entirely in Java and is thus portable to a wide variety of platforms, requiring only the Java Runtime Environment.