Ground speed measurement is required in many agricultural machinery operations. There are a number of techniques for the determination of the ground speed; however, each of these methods has some disadvantages. It is known that a GPS receiver is capable of calculating travel speed; however, no study has been reported on the performance of low-cost GPS receivers in measuring the ground speed in agricultural machinery operations. The objective of this work was to study the effectiveness of low-cost GPS receivers for measuring ground speed. Computer programs were written to read, store, and process the GPS data from two different low-cost GPS receivers. Differential correction was not used in the study since there was no correction service in the study area. A very strong relationship between the average GPS speeds and the average calculated speeds was found in the study (R-2 > 0.99). Also, the results showed that the GPS receivers followed the speed change quite well. GPS receivers can be used to determine both the position and the speed of the agricultural machinery. In this way, there is no need to use a separate speed sensor leading to simpler and more affordable instrumentation systems. In conclusion, low-cost GPS receivers can be confidently used to measure the ground speed in agricultural machinery operations. (c) 2006 Elsevier B.V. All rights reserved.