To make bovine embryo sexing under farm conditions more feasible we developed a simplified protocol utilizing manual biopsy and detection of the Y chromosome directly from polymerase chain reaction (PCR) reaction tubes. Twenty-four embryos (morulae and blastocysts) were biopsied manually into 2 to 4 samples. One sample of each original embryo was diagnosed for sex, based on restriction fragment length polymorphism of PCR-amplified DNA of the ZFX/ZFY locus. The remaining 44 samples were diagnosed using the tube detection assay. In this assay the biopsies were pipetted into 0.5 -ml reaction tubes containing lysis mixture, incubated 10 to 60 min at 37 degrees C and inactivated 10 min at 98 degrees C. Then the PCR mixture was added containing buffer, DNA polymerase, ethidium bromide and primers designed to amplify the highly repeated btDYZ-1 region of the bovine Y chromosome. After 50 cycles of PCR, the reaction tubes were examined under UV illumination for pink fluorescence indicating the presence of Y-chromosomal DNA. All sexing results from the replicates were in agreement with the ZFX/ZFY assay, with 12 of the original embryos diagnosed as females and 12 as males. We conclude that highly efficient and accurate PCR-sexing of embryos can be accomplished without the use of micromanipulators, control primers and electrophoresis. The 2 reaction mixtures needed for sex diagnosis can be stored at -20 degrees C and -196 degrees C, respectively. The tube detection assay minimizes the risk of carryover contamination by previously amplified products as there is no need to open the tubes following PCR.