After severe deterioration of the exterior marble architectural elements was observed in the Schenectady, New York, City Hall, a study was undertaken to analyze the causes and extent of the deterioration, as well as methods for its arrest and control. The following techniques were employed: optical microscope with photomicrographic dispersive staining capability; scanning electron microscope (SEM) and computer-based energy-dispersive x-ray microanalyzer (EDXA), ion chromatography, electron microprobe, and environmental pollutants data. Results showed that deterioration of marble was caused by a constant direct chemical attack by sulphuric acid, and that neither nitric acid nor acid precipitations played a major role in the weathering process. The programme for cleaning and conservation of both the exterior and interior marble consisted of: a) thorough cleaning of the exterior marble using low-pressure water washing with the use of chemical cleaning agents in badly deteriorated areas; b) cleaning of the interior marble using liquid cleaning agents and poultices, c) preparation of a long-term conservation/maintenance/repair programme to arrest future deterioration. Bibliography.