Ammonium records from 3 ice cores, 20D and GISP2 (Greenland) and Mt. Logan (Yukon), covering the period from 1750 to the 1980s are analyzed. For each data set, samples with NH4+ concentrations greater than one standard deviation above the mean value also tend to be enriched in NO3− and K+, similar to the chemical composition of aerosols from aged biomass burning plumes. We believe the NH4+ spikes originate from biomass burning events. There is not a one to one correspondence between documented large fires and NH4+ spikes, nor are specific annual layers with elevated NH4+ concentrations often found in more than one core. However, frequency of NH4+ spikes increase during periods of more extensive and intensive biomass burning in the NH4+ source areas for the ice core sites. The 20D and GISP2 records are characterized by increased spike frequency from 1790 to 1810 and from 1830 to 1910. This latter time coincides with a period of increased biomass burning documented in the historical fire records for northern North America. In contrast to both Greenland ice core records, the Mt. Logan NH4+ record shows periods of increased spike frequency from 1770–1790, 1810–1830, 1850–1870 and 1930–1980. The poor agreement between the Mt. Logan record and the records from Greenland suggests that another source area, perhaps Siberia, may be the dominant summertime source area for NH4+ spikes in Mt. Logan snow.