Curium is a byproduct of plutonium production activities and results from the successive capture of neutrons by plutonium and americium, generally in nuclear reactors. In the environment it is found where releases from weapons production facilities have caused localized contamination. It is mainly used for research activities and monitoring of radiochemical procedures. A new standard solution of 244Cm was developed and will be disseminated at NIST as SRM 4320b. The certified massic activity for 244Cm in radioactive equilibrium with 240Pu was obtained by 4ηαβ liquid scintillation (LS) spectrometry with three commercial LS counters. Confirmatory measurements were performed by high-resolution HPGe gamma-ray spectrometry. The combined standard uncertainty (k = 2) on the standardization is 1.4 %. The certified value of the massic activity for SRM 4320b was in agreement with that for the previously issued SRM 4320a to within 1.0 %.