T-wave alternans (TWA) manifests on the surface ECG as a pattern of alternating amplitude T-waves, typically in the microvolt range. Consequently, TWA is usually invisible at standard ECG display scales and must be detected using signal processing methods. There is a predictive relationship between TWA and sudden cardiac death, so proper detection and estimation may contribute to clinical decision-making. The objective of the 2008 Physionet/Computers in Cardiology Challenge was to estimate the magnitude of TWA in a dataset of 100 multi-lead ECGs. We used a modified moving average method (MMA) to detect and estimate TWA. We found that the TWA magnitude ranged from to 1.3 to 256.9 μV (43.9 ± 49.7 μV). The Kendall rank correlation coefficient obtained for the challenge was 0.451. In conclusion, the MMA method can be used for detection and estimation of TWA, though additional work could further improve the method.