Concentrations of Hg and Se were determined for a total of 125 Common Loon (Gavia immer) eggs collected from lakes in Alberta, Saskatchewan, Ontario, Quebec, New Brunswick and Nova Scotia, Canada between 1972 and 1997. Resulting data were compared to Hg and/or Se concentrations known or suspected to cause reproductive impairment in birds. Organic (methyl) Hg analyses were also performed on a subset of 24 loon eggs. Thirty-nine of 125 eggs had total Hg levels exceeding those (0.6 microg g(-1) ww, or approximately 2.5 microg g(-1) dw) previously reported to be associated with reproductive impairment in common loons (Barr, 1986), and 9 of 125 eggs had Hg concentrations higher than the level associated with reproductive impairment in birds generally 1 microg g(-1) ww; (Thompson, 1996). Selenium concentrations in loon egg samples were less than levels known to cause reproductive impairment in birds. A weak but significant positive correlation was observed between egg-Hg and -Se concentrations (r = 0.511, p < 0.05). On average, methylmercury accounted for about 87% of total Hg in 24 eggs analysed for both total and organic Hg. In this subset of eggs, the relationship between organic (methyl) Hg and Se was significant (r = 0.538, p = 0.007) while that found between inorganic Hg and Se in the same eggs was not significant (r = 0.353, p = 0.091). This relationship was unexpected and was contrary to relationships established for organic and inorganic Hg vs. Se in adult loon liver and kidney tissue (Scheuhammer et al., 1998b).