Concentrations of IgG, IgM and IgA were measured in the serum, nasal secretions and lachrymal secretions of suckled newborn lambs. The major immunoglobulin constituent of precolostral serum was IgM. Maternal immunoglobulins, of which IgG was predominant, reached peak values on day 1 of life and then declined over the next 3 weeks. Half lives were calculated as: IgG, 13-7 days; IgM, 4-1 days; and IgA 1-8 days. No immunoglobulin was detectable in nasal or lachrymal secretions prior to sucking but IgG was present in all samples of these secretions obtained approximately 24 hr after first sucking. IgG was present in nasal washings from suckled lambs, reared either naturally or on immunoglobulin-free milk substitute and levels declined as the lambs grew older. IgM and IgA did not appear consistently in the secretions until lambs were 2-3 weeks old. It was concluded, therefore, that colostral IgG reaches the nasal and lachrymal secretions of the newborn lamb. However, because the ewes in this experiment had only low serum titres, no maternal antibody to parainfluenza 3 virus (PI3) was detected in the nasal secretions of the lambs, although non-specific inhibitors were present. It is suggested, however, that low levels of maternal antibody in the secretions may play a valuable role in preventing respiratory virus infections of young ruminants before active local production of IgA and IgM begins at 2 to 3 weeks of age.