The evaluation of pre- and intraoperative corneal thickness is of great importance in photorefractive surgery and in planning phototherapeutic treatments. The authors evaluated 14 eyes with Humphrey ultrasonic pachymeter Model 855 during photorefractive keratactomies (PTK). All treatments were performed with the Aesculap Meditec MEL 60 ArF excimer laser. The preoperative uncorrected visual acuity averaged 0.078 +/- 0.068. The average of preoperative correction used to obtain the best corrected visual acuity was: -6.11 +/- 3.70. The average preoperative corneal thickness was found at 548.14 +/- +/- 24.58 microns; the average thickness of the mechanically removed epithelium was: 51.5 +/- 1.49 microns. After PRK the corneal thickness decreased to 440.78 +/- 33.2 microns. The thickness of the photoablated corneal tissue was on the average 55.86 microns measured by the ultrasound pachymeter. The pachymeter values correlated well with the average of 53.21 +/- 30.19 microns thickness change calculated by the excimer laser combi modul display monitor. The authors conclude, that ultrasound pachymeter is suitable for evaluating pre- and intra-operative corneal thickness. Echobiometric pachymetry is valuable in planning and executing phototherapeutic treatment. It permits the surgeon to assess intraoperatively the thickness of the already ablated corneal tissue and reduce the risk of postoperative refractive changes. The method is also suitable for controlling the photorefractive calibration of the excimer laser.