"Breachers" are a unique military and law enforcement population because they are routinely exposed to low-level blast (LLB) during training and operations. This repeated exposure has been associated with symptoms similar to that of sports concussion. This study examined effects of repeated exposure to LLB during an explosive entry course. Twenty-one members of the New Zealand Defence Force volunteered for this study. Serum samples, neurocognitive performance, and self-reported symptoms were periodically measured before, during, and after a 2-week course. Serum concentrations of three biomarkers, ubiquitin C-terminal hydrolase-L1, αII-spectrin breakdown product, and glial fibrillary acidic protein, were determined with sandwich enzyme-linked immunosorbent assays, and rank scores were derived using the area under the curve (relative to baseline) for each subject. Neurocognitive performance was measured with a computer-based test battery, and symptoms were assessed by paper-based inventory. There was a significant relationship (p<0.05) between composite biomarker and neurocognitive performance and between neurocognitive performance and symptoms. The individuals with the five highest (Top 5) and lowest (Bottom 5) composite biomarker scores were identified and compared using Wilcoxon's rank-sum test. The Top 5 had significantly longer reaction times and lower percent correct on neurocognitive performance and an increase in symptom reporting. The difference between individuals expressing the highest biomarker load during breacher training (Top 5) and those with the lowest biomarker load (Bottom 5) is reflected in neurocognitive performance deficits and self-reported symptoms. This suggests a measureable degree of brain perturbation linked to LLB exposure. Follow-up studies are underway to expand upon these results.