Human basal cell carcinoma (BCC) offers a unique opportunity to assess directly the microvascular abnormalities in a human cancer in vivo. Our objectives were to assess angiogenesis, perfusion, and changes in small solute exchange kinetics. The microcirculation of BCC and a normal (control) skin site was studied in 15 patients by laser Doppler fluximetry and videoangiography after rapid i.v. fluorescein injection. Microvascular morphometry was analyzed off line. Sodium fluorescein accumulation/clearance was recorded for 30 min, and fluorescence intensity (FI) was quantified by computer analysis of videotape image gray levels. In BCCs, the microvascular area fraction was 2.6-fold greater, microvessel length density 2.0-fold greater, average vessel image width 2.1-fold greater, and red cell flux 3.9-fold greater than in control sites (P < 0.01, paired t tests). The initial rate of rise of FI over 10 s was approximately 3-fold greater in BCC than control and correlated with vascular area fraction and red cell flux. Tissue then equilibrated faster in BCC, rate constant -(13.0 +/- 5.6) x 10(-3) s(-1) (mean +/- SD), than controls -(5.3 +/- 1.7) x 10(-3) s(-1), and plasma clearance was 2.6-fold higher in BCC than controls (P < 0.01, paired t test). Similarly, the rate constant of the subsequent clearance phase was approximately 2-fold greater in BCC, -(0.53 +/- 0.19) x 10(-3) s(-1), than controls, -(0.27 +/- 0.22) x 10(-3) s(-1) (P < 0.01). Removal rate constants were an order of magnitude slower than accumulation rate constants. The results demonstrate angiogenesis, increased perfusion, and a more rapid exchange of small solute in human BCC. FI itself is rejected as an index of permeability to small solutes (cf. 29) because it depends also on blood flow, endothelial area, microvascular volume, and interstitial fluid volume.