tEvaluation of sperm morphology is a fundamental component of semen analysis, but itsreal significance has been obscured by a plethora of techniques that involve fixation andstaining procedures that induce artefacts. Here we describe TrumorphP ®, a new method forsperm morphology assesment that is based upon examination of wet preparations of livingspermatozoa immobilized by a short 60◦C shock using negative phase contrast microscopy.We have observed samples from five animals of the following species: bull, boar, goat andrabbit. In every case, all the components of the sperm head and tail were perfectly defined,including the acrosome and midpiece (in all its length, including cytoplasmic droplets). Arange of morphological forms was observed, similar to those found by conventional fixedand stained preparations, but other forms were found, distinguishable only by the opticsused. The ease of preparation makes it a robust method applicable for analysis of livingunmodified spermatozoa in a range of situations. Subsequent studies on well-characterizedsamples are required to describe the morphology of potentially fertilizing spermatozoa.