Human scalp hair retains the past dosage history over a rather long period of time, acting as 'tape-recorder'. Each 1-cm length of hair contains the drug approximately corresponding to the amount ingested over a 1-month period when the hair is cut into 1-cm lengths successively from the scalp end. However, the hair growth rate is variable both within and between subjects and the hair has its own growth cycle. Therefore, the validity of obtained results must always be considered cautiously, especially in relation to whether resting-stage hair might have been sampled. It has been found that antimicrobial quinolones are detectable in hair, even after a short exposure to them, and serve as time marker for estimating the growth rate itself and the stage of hair. By analysing the axial distribution of ofloxacin-one of the most frequently prescribed quinolone derivatives in Japan-along the hair shaft, the 'tape-speed' and 'uniformity of tape-running' of a single hair can be estimated. Research into cigarette-smoking behavior necessitates accurate measurement of smoking habit. It has been found that the nicotine content in hair is proportional to the number of cigarettes consumed daily. Moreover, the cm-by-cm analysis of axial nicotine distribution along the hair shafts revealed the concentrations of nicotine approximately proportional to the month-by-month self-report on daily-consumed cigarettes in a subject who participated in a smoking-cessation program.