Jewish merchants played an important role in Polish trade. This issue has been researched by many historians, including I. Schiper, Z. Guldon, J. Morgenstern and J. Malecki. The article explores the intense activity of Jewish merchants from Chelm observable in the second half of the 16th c. In the Central Archives of Historical Record in Warsaw there are customs declarations of Jewish merchants from Chelm, submitted to the customs houses in Lublin, Lvov and Busko. As to the towns with which Chelm merchants had trade connections, most declarations concern Lublin (62), then there was Lvow (24), Gniezno (14) Chelm (2) and Kazimierz (1). There are also 9 declarations from the Lublin customs house, specifying neither the town from which the commodities were expedited nor their destination, and 2 declarations from the customs house in Busko lacking the destination. Declarations contain information on the town to which a given tradesman carried his commodity, on its quantity, on the customs payable and on whether it was paid. An analysis of the declarations has led to the conclusion that most of them were connected with fairs. For example, out of 62 declarations concerning Lublin 59 were connected with fairs. The majority of merchants came to the winter fair on the 2nd of February (35 declarations, 59%); other fairs attracted relatively fewer tradesmen. The same concerned Gniezno, with 12 declarations (86%) connected with the spring fair on the 23rd of April and 2 (14 %) with the summer fair on the 24th of July. The situation in Lvov was slightly different, yet the majority of declarations (66%) can be connected with fairs. As to the distribution of commodities, Lublin and Gniezno were common destinations for hides. Declarations mention large quantities (several thousand) of cowhides, goatskins, sheepskins etc. Other goods include wax, suet and honey. The most important commodities brought to Lublin and Chelm were woollen textiles of different types in huge quantities, then barrelled herring, ironmongery, scythes, sickles, nails, homespun coats and stall assortment for a fixed sum of money. The declarations indicate that Chelm merchants often did business in various towns. For instance, the Jew Saul Nowakowicz in 1565 was in Lvow at St Agnes' fair (the 21st of January) and in May returned from Gniezno from St Adalbert's fair (the 23rd of April). This example, which is one of many, corroborates many Polish historians' findings concerning the zones of exchange in the Polish territories. Chelm merchants participated in the pendulum-like movement between Lvov in the south and Gniezno in the north-east, with Chelm and Lublin in between. To sum up, the analysis of customs declarations has shed new light on the issue of trade in Chelm. Although the data and sources pertaining to the subject are scarce, the declarations confirm that the town was a significant trading centre and that the exchange with other towns was developing successfully.