OpenFileDialog openDialog = new OpenFileDialog();
            openDialog.FileName = "Книга1";
            openDialog.Filter = "Файл Excel|*.XLSX; *.XLS";
            openDialog.ShowDialog();
            try
            {
                objApp1 = new ApplicationClass();
                objBook1 = objApp1.Workbooks.Add(openDialog.FileName);
                objSheet1 = objApp1.ActiveSheet as Worksheet;
                excells = null;
                int row = 1;
                string nstr = "нет товара";
                string t = objSheet1.get_Range(String.Concat("A", row), String.Concat("A", row)).Value2.ToString().Trim();
                while (objSheet1.get_Range(String.Concat("A", row), String.Concat("A", row)).Value2.ToString().Trim().Equals(""))
                {
                    if (objSheet1.get_Range(String.Concat("A", row), String.Concat("A", row)).Value2.ToString().Trim() == "Марс")
                        nstr = row.ToString();
                    row++;
                }
                textBox1.Text = nstr;
            }
            catch (Exception ex)
            {
             MessageBox.Show("Ошибка: " + ex.Data + ex.Message, "Ошибка при считывании файла",
             MessageBoxButtons.OK, MessageBoxIcon.Asterisk);
            }
            finally
            {
                objBook1.Close(" ", Filename, null);
                objApp1.Quit();
                objSheet1 = null;
                objApp1 = null;
                GC.Collect();

....
                string nstr = "нет товара";
                int lastrow = objSheet1.Cells.SpecialCells(XlCellType.xlCellTypeLastCell).Row;
                for (int row=1;row<=lastrow;row++) 
                {
                    if (objSheet1.get_Range(String.Concat("A", row), String.Concat("A", row)).Value2.ToString().Trim() == "Марс")
                        nstr = row.ToString();
                }
                textBox1.Text = nstr;
            }
.............