Bovine collagen implants are in widespread use for the correction of soft tissue deficiencies. A small portion of the population responds adversely to these implants, evidenced by either positive skin tests or treatment site reactions. Antibodies against bovine collagen implants have been detected in the sera of virtually all patients with adverse treatment reactions and in small percentages of untreated individuals and treated individuals without adverse reactions. In this study we examined the levels of anti-bovine collagen implant antibodies in 150 individuals prior to bovine collagen implant therapy and then monitored these patients for adverse reactions to skin tests and bovine collagen implant treatments. Statistical analyses were performed to determine the value of pretreatment serology in predicting positive skin tests or adverse reactions. It was determined that individuals with greatly elevated levels (greater than 2 standard deviations [SDs] above the mean reactivity of pretreatment sera) of anti-bovine collagen implant antibodies prior to treatment were approximately sixfold more likely to suffer adverse reactions than patients with no elevation of antibodies prior to treatment.