Cats (n = 6) were administered dexmedetomidine (DEX) and medetomidine (MED) at three different dose levels in a randomized, blinded, cross-over study. DEX was administered at 25, 50 and 75 microg/kg (D25, D50 and D75), corresponding to MED 50, 100 and 150 microg/kg (M50, M100 and M150). Sedation, analgesia and muscular relaxation were scored subjectively. Heart and respiratory rates and rectal temperature were measured. Corresponding doses of DEX and MED were compared. Effects were also compared between dose levels for each compound. At dose level 2 (D50-M100), the duration of effective clinical sedation was significantly shorter after DEX (202.5 +/- 16.0 min) than after MED (230.0 +/- 41.2 min). Proceeding from D50-M100 to D75-M150, the duration of effective clinical sedation was increased more after DEX (by 57.5 +/- 38.4 min) than after MED (by 14.2 +/- 41.9 min) Increasing from D50-M100 to D75-M150, heart rate was further decreased after DEX (by 8.1 +/- 13.4%) but not after MED. There was no statistically significant difference between corresponding doses of DEX and MED for any of the other parameters studied. Changes in sedation, analgesia and muscular relaxation were dose-dependent. It was concluded that anaesthetic effects of medetomidine in cats are probably due entirely to its d-isomer and that dexmedetomidine at 25, 50 and 75 microg/kg induces dose-dependent sedation, analgesia and muscular relaxation of clinical significance in cats.