We measured immunoglobulins in the sera of 33 patients on days 1, 3, 6, 10, and 17 and three to four weeks after surgical operations (mostly hysterectomy or appendectomy) or (six patients) after spinal injury. In the absence of infection or blood transfusion, IgG usually decreased slightly and transiently after hysterectomy or appendectomy, as did IgA or IgM after hysterectomy. IgD concentrations showed no consistent changes, but in one patient after hysterectomy and with minimal infection IgD concentration decreased sharply, which contrasted with significant and early increases in IgG, IgA, and IgM. IgD concentration was not correlated with type of operation, presence of infection, or changes in the other immunoglobulins. IgE concentrations either die not change or, in some patients, increased or decreased initially, after operation. We conclude that immunoglobulin concentrations in serum are subject to multiple, unpredictable influences after trauma.