Tradescantia paludosa (Spiderwort) clone 03, an extensively cultivated experimental plant for cytological studies, has been utilized exclusively for the present investigation. Year-round growth and reproduction of this plant can be maintained in the greenhouse with supplemented artificial light during the short-day season thus facilitating the uninterrupted supply. Taking the advantages of high degree of synchrony and differential sensitivity of the meiotic stages, a short-term bioassay was developed for testing environmental mutagens. This was done by treating the synchronized, sensitive early prophase I meiotic chromosomes and observing the damaged chromosomes in the form of micronuclei in the sychronized early tetrad stage in order to attain the highest efficiency. This test is called Tradescantia Micronucleus (Trad-MCN) Bioassay and has been utilized to screen a group of chemicals in gaseous or liquid forms and monitor the air pollutants at some chosen sites. Of 16 chemicals tested, 8 had relatively higher micronucleus frequencies (0.01 level of significance) than their controls. Of 11 sites monitored, 3 sites showed higher micronucleu frequencies than their controls. According to these results, the TRAD-MCN bioassay showed high efficiency and versatility. It is suitable for preliminary screening of environmental pollutants and in situ monitoring.