Repeated exposure to solar ultraviolet radiation results in premature skin aging due, in part, to the degradation of dermal collagen by fibroblast collagenase (matrix metalloproteinase 1 [MMP-1]). We have established TaqMan^™ reverse transcription (RT) polymerase chain reaction (PCR) systems to quantify the messenger RNA (mRNA) expression of MMP-1 and its specific inhibitor TIMP-1 in human buttock skin exposed in vivo to solar simulated radiation (SSR). A time-course study (n = 6) with two minimal erythema doses (MED) of SSR showed maximal induction of MMP-1 and TIMP-1 at 24 h. A dose–response study (n = 6) sampled at 24 h revealed that doses of about 1 MED were necessary to induce expression of MMP-1 mRNA, and our data suggest that the response is saturated at about 2 MED. We also investigated SSR-induced gene expression in the dermis and epidermis separately (n = 5). MMP-1 was present in both tissues, but TIMP-1 was only detected in the dermis. In general, we could only measure MMP-1 mRNA in the nonirradiated control skin of volunteers who were smokers. We hypothesize very large interpersonal variation with MMP-1 induction compared with TIMP-1 which was detected in all the control sites. This suggests a lack of relationship between MMP-1 and TIMP-1 mRNA expression. The large donor variability for MMP-1 in all the studies demonstrates that it is important to analyze gene expression individually.