Although sentinel lymph node (SLN) biopsy is rapidly becoming the standard of care for small breast cancers the optimal radiocolloid injection technique remains controversial. We report our experience with sequential dermal-peritumoral radiocolloid injection that takes advantage of both techniques. One hundred eighteen patients with clinical stage T(is), T1, T2 and N0 breast cancer underwent SLN biopsy at the University of Florida. Twelve to 18 hours before surgery patients received either an injection of 0.5 to 1.0 mCi 50:50 filtered:unfiltered technetium sulfur colloid into the dermis overlying the tumor and/or a peritumoral injection of a 3 to 4-mCi of radiocolloid 30 minutes later. Dynamic lymphoscintigraphy was performed and the topographical location of all imaged lymph nodes was marked on the skin. The next morning the surgeon utilized a hand-held gamma probe to remove all SLN(s) defined as any lymph node with radioactive counts 10 per cent or more of the ex vivo counts of the most radioactive SLN [internal mammary (IM) nodes were not removed]. The SLN identification rate was 98.5 per cent (3 IM nodes) for dermal injection (d.), 83.3 per cent (1 IM node) for peritumoral injection (p.), and 100 per cent (14 IM nodes) for sequential dermal-peritumoral injection (d.p.) (p < 0.05 DP versus D). Sequential d.p. 50:50 filtered:unfiltered technetium sulfur colloid injection results in a rapid, high SLN identification rate that persists until surgery the next morning. Delineation of nonaxillary SLNs may lead to more accurate breast cancer staging and may also influence the delivery of IM node radiation.