BACKGROUND Phototesting based on a single exposure to a divergent ultraviolet B (UVB) beam with radially decreasing UVB doses can be used to determine an individual's minimal erythema dose (MED). Laser Doppler perfusion imaging (LDPI) data can be combined with dosimetry data to produce objective dose-response plots in addition to the MED. The aim of this study was to investigate whether the divergent beam protocol could be used to demonstrate and quantify the anti-inflammatory effects of clobetasol diproprionate (Dermovate), pharmaceutical-grade acetone and a gel vehicle, applied after skin provocation by UVB. METHODS Sixteen Caucasian subjects were illuminated with the divergent beam on three areas close together on the left side of their upper backs. Two of the provoked areas on each subject were treated with acetone, gel vehicle or Dermovate, and one area was left untreated as a control. Skin blood perfusion was assessed 6 and 24 h after UVB illumination using LDPI. The reaction diameter, the mean perfusion, and the average dose-response plots for each group and treatment were extracted from the LDPI data. RESULTS Application of the topical steroid clobetasol diproprionate after UVB provocation markedly decreased the inflammatory response. Acetone and the gel vehicle also showed mild anti-inflammmatory effects in two of the parameters but not for the mean perfusion response. The mean diameter differences between controls and treated reactions had predominantly positive 99% confidence intervals. Analysis of the dose-response data at doses higher than the MED showed a linear relationship (0.89<or=R2<or=0.98) for all reactions but with lower gradients in treated reactions, mostly marked for clobetasol diproprionate. CONCLUSIONS The divergent beam protocol can be used to demonstrate and quantify the effects of topical agents on the UVB reaction, in terms of reaction diameter, mean perfusion and changes in dose-response characteristics. The dose-response approach seems to be applicable even in diagnostic testing of an individual patient's response to UVB.