This study had two aims. Firstly, to determine the associations of month of recording (MOR) and days in milk (DIM) with somatic cell count (SCC), milk urea concentration (MU) and milk production traits (i.e. test-day milk yield, TDM; milk protein percentage, PP and milk protein yield, PY). Secondly, to evaluate the associations among SCC, MU and milk production traits by analyzing individual monthly test-day records for dairy cows raised in the Czech part of the Czech Republic. A total number of 33,881 individual test-day milk records involving 15,565 dairy cows for a 12-month period between January and December 2001 enrolled in DatabaseComputerCenter belonging to Czech Moravian Breeders´ Corporation, Inc., Hiradistko, The Czech Republic were used. Data were analyzed using General Linear Model procedure (GLM) using Statistical Analysis System (SAS, 2004).  The MOR and DIM had highly significant (P<0.001) effects on the studied traits. The SCC reached the maximum level in September (504,000) associated to the lowest TDM (19.9 kg) and the lowest SCC in December (320,000) and February (335,000 cell/ml). Least squares means of TDM, categorized by 30-d increments of DIM, paralleled reversible changes in PP and followed a curvilinear shape. SCC reached to the peak in the 2^nd and 3^rd months of lactation then decreased gradually to the end of lactation. MU was lower (30.5 mg/dl) during the first 30 DIM compared with all other DIM categories.  The statistical analysis of TDM, PY and SCC by MU showed that as MU increased, TDM, PY increased and SCC decreased.  MU, SCC, PP and PY were significantly different among TDM categorized.  Each of PP and SCC measures inversely associated with TDM, meanwhile MU paralleled change with TDM.  Somatic cell count measures showed a paralleled change with PP.  The effects of environmental variables and associations among traits must be taken into consideration when cows are evaluated.