In normal pregnancy (NP), voltage [K_v] and ATP [K_ATP]-sensitive potassium (K) channel mRNA is expressed in the placental vasculature [1]. We have shown that K channels are important in the control of placental vascular reactivity in NP [2] and in pregnancies affected by intrauterine growth restriction (IUGR) [3]. However, there are no data on gene expression of K channels in the NP and IUGR placental vasculature. We aimed to determine K channel gene expression in NP and IUGR placental tissue. Placental homogenate, chorionic plate arteries and veins (NP; N=6: IUGR; N=5) were obtained after vaginal delivery or Caesarean section at term. Tissue sampling, total RNA isolation and cDNA production were performed as described previously [4]. K channel expression was assessed using SYBR Green 1 quantitative PCR. Channel sequences were derived from GenBank with reference to BLAST and primers designed with Beacon designer software. Each sample (1μl) was run as quadruplicate reactions with a passive reference dye. Quantification was performed using sample cycle threshold values to calculate initial input amounts from a standard curve of cDNA generated using a human reference RNA and normalised to a human reference cDNA calibrator. Expression was assessed relative to the calibrator. In IUGR placental chorionic plate arteries and veins showed similar expression levels of K_v2.1; placental homogenate expression was increased compared to arteries only. Similar expression patterns were seen for K_v9.3 and K_IR6.1. In NP a similar pattern of expression was observed with K_v2.1; similar arterial and venous expression; raised expression in placental homogenate compared to arteries only. With K_v9.3 and K_IR6.1, expression levels were similar in arteries, veins and placental homogenate. When comparing IUGR and NP gene expression directly, only venous expression of K_v2.1 was increased (Fig 1; P<0.05 Mann Whitney U test). We found variable placental K-channel expression in NP and IUGR. Only venous expression of K_v2.1 was increased in IUGR versus NP. Aberrant K_v channel expression may contribute to altered placental vascular resistance associated with IUGR pregnancies.