Metaphase-arresting agents amiprophos-methyl (APM), colchicine (COL) and cell cycle-synchronization (CCS) with APM and hydroxyurea (HU) were tested for growth, metaphase index and cytogenetic abnomalities in barley (Hordeum vulgare cv. Bornova-92). Seeds were germinated for 2 days and then seedlings were treated with 8 mu M (2.4 mg/L) APM for 2 h or 1.25 mM (0.5 g/L) COL or synchronized (CCS) with 1.25 mM (95 mg/L) hydroxyurea for 18 h and with 4 mu M (1.2 mg/L) APM for 2 h. APM and CCS caused metaphase indices 12.57 and 38.82% respectively. COL also arrested metaphase (14.10%) but also resulted in nuclear aberrations (11.15%). After removal of APM and CCS, cells were released to grow and divide. However, COL caused irreversible effects on cell division and growth and meanwhile was shown to be effective for micronucleus formation.